Statutory guidance

SR2018 number 7: new and existing, low risk, stationary medium combustion plant

Updated 26 February 2026

Applies to England

The Environmental Permitting (England & Wales) Regulations 2016

Introductory note

This introductory note does not form a part of these standard rules.

When referred to in an environmental permit these rules will allow the operator to operate one or more new or existing medium combustion plant (MCP) which may be in an Air Quality Management Area unless the combustion plant is references in a relevant Air Quality Plan.

The limits of the permitted activity are that:

• all new MCP shall operate with a net rated thermal input equal to or greater than 1 MWth and less than 20 MWth
• all existing MCP shall operate with a net rated thermal input equal to or greater than 5 MWth and less than 20 MWth
• the total aggregated net rated thermal input of combustion plant of any size at the permitted location must be less than 50 MWth
• MCP are permitted to burn gas oil, gas oil substitutes , natural gas, hydrogen, biogas or other gaseous fuels
• MCP must use single fuel combustion except blends of natural gas and hydrogen or where gas oil or gas oil substitutes are used as a back-up fuel in boilers for planned maintenance or emergency use for less than 500 hours per year
• any activities undertaken must not include activities to which Schedule 24 (Energy Efficiency Directive) of the Environmental Permitting Regulations applies
• all MCP must meet the minimum distances criteria specified in these standard rules from any MCP to a protected habitat depending on the plant type, fuel type and technology type
• no MCP shall generate electricity as a generator under these standard rules unless the power is used as a ‘back-up generator’

Words and expressions used in this introductory note and these standard rules shall have the meanings given in section 4.4, as appropriate.

End of introductory note

Rules

1. Management

1.1 General management

1.1.1 The operator shall manage and operate the activities:

(a) in accordance with a written management system that identifies and minimises risks of pollution, so far as is reasonably practicable, including those risks arising from operations, maintenance, accidents, incidents, non-conformances and those drawn to the attention of the operator as a result of complaints; and

(b) using sufficient competent persons and resources.

1.1.2 Records demonstrating compliance with rule 1.1.1 shall be maintained.

1.1.3 Any person having duties that are or may be affected by the matters set out in these standard rules or the permit shall have convenient access to a copy of the permit and the rules.

2. Operations

2.1 Permitted activities

2.1.1 The operator is only authorised to carry out the activities specified in Table 2.1.

Table 2.1 activities

Activity reference	Description of specified activity	Limits of specified activity
New and existing MCP	The operation of new MCP with a net rated thermal input greater than or equal to 1 MWth and less than 20 MWth. The operation of existing MCP with a net rated thermal input greater than or equal to 5 MWth and less than 20 MWth. The specified activities may include limited operating hours MCP.	The only fuel used by the MCP shall be gas oil, gas oil substitutes, natural gas, hydrogen, biogas or other gaseous fuels. The total aggregated net rated thermal input of combustion plant of any size or type at the permitted location must be less than 50 MWth. MCP must use single fuel combustion except blends of natural gas and hydrogen or where gas oil or gas oil substitutes are used as a back-up fuel in boilers for planned maintenance or emergency use for less than 500 hours per year. The activities shall not include any activities to which Schedule 24 (Energy Efficiency Directive) of the EP Regulations applies. No MCP shall generate electricity as a generator under this rule set unless the power is used as an excluded back-up generator. The MCP may be in an Air Quality Management Area unless the combustion plant is referenced in a relevant Air Quality Plan.

2.2 The permitted location

2.2.1 No MCP shall be operated other than at its location as specified by grid reference in Appendix A.

2.2.2 The activities shall be carried out in accordance with the following limits:

(a) all boilers shall be at least the minimum protective distance between the MCP and a protected habitat depending on the primary fuel and whether they are new, existing or new existing MCP, as specified in table 2.2.

(b) all engines or turbines shall be at least the minimum protective distance between the MCP and a protected habitat depending on the primary fuel and whether they are new, existing or new existing MCP, as specified in table 2.3.

(c) all engines operating as a back-up generator shall be at least the minimum protective distance between the MCP and a protected habitats depending on the primary fuel and whether they are new, existing or new existing MCP, as specified in table 2.4.

Table 2.2 – Boilers

Primary fuel	Type of MCP	Minimum protective distance to a protected habitat in metres
Biogas	New MCP or new existing MCP	3,000
Gas oil or Gas oil substitute	New MCP or new existing MCP	800
Natural gas	New MCP or new existing MCP	500
Hydrogen	New MCP	500
Other gaseous fuels	New MCP or new existing MCP	1,700
Biogas	Existing MCP	4,000
Gas oil or Gas oil Substitute	Existing MCP	800
Natural gas	Existing MCP	800
Hydrogen	Existing MCP or new existing MCP	1,300
Other gaseous fuels	Existing MCP	1,800

Table 2.3 – Engines or Turbines

Primary fuel	Type of MCP	Minimum protective distance to a protected habitat in metres
Biogas	New MCP or new existing MCP	4,000
Gas oil or Gas oil substitute	New MCP or new existing MCP	1,500
Natural gas	New MCP or new existing MCP	1,000
Hydrogen	New MCP	1,000
Other gaseous fuels	New MCP or new existing MCP	2,500
Biogas	Existing MCP	5,000
Gas oil or Gas oil substitute	Existing MCP	1,500
Natural gas	Existing MCP	1,600
Hydrogen	Existing MCP or new existing MCP	2,500
Other gaseous fuels	Existing MCP	2,500

Table 2.4 Engine operating as a back-up generator

Primary fuel	Type of MCP	Minimum protective distance to a protected habitat in metres
Biogas	New MCP or new existing MCP	150
Gas oil or Gas oil substitute	New MCP or new existing MCP	250
Natural gas	New MCP or new existing MCP	100
Hydrogen	New MCP	100
Other gaseous fuels	New MCP or new existing MCP	150
Biogas	Existing MCP	200
Gas oil or Gas oil substitute	Existing MCP	250
Natural gas	Existing MCP	100
Hydrogen	Existing MCP or new existing MCP	150
Other gaseous fuels	Existing MCP	150

2.3 Operating techniques

2.3.1 The activities shall be operated using the techniques and, in the manner, described in the following sub-paragraphs:

(a) each MCP must be operated in accordance with its manufacturer’s instructions and records must be made and retained to demonstrate this.

(b) the operator must keep periods of start-up and shut down of each MCP as short as possible.

(c) there must be no persistent emission of ‘dark smoke’ as defined in section 3(1) of the Clean Air Act 1993.

(d) the stack shall be vertical and unimpeded by cowls or caps unless that is not practicable.

(e) the operator must keep periods operating dual fuel boilers on back-up gas oil or gas oil substitutes as short as possible.

(f) a limited operating hours MCP, which is an excluded generator, may only be operated for the sole purpose of maintaining power supply to the permitted location during an emergency on or at the permitted location and it may not participate in any balancing services including triad avoidance operations.

(g) a limited operating hours MCP, which is an excluded generator, may only be operated for the sole purpose of testing for no more than 50 hours a year.

(h) limited operating hours MCP must be operated:

   (i) for no more than 750 hours operation in any single year; and

   (ii) for no more than 500 hours in a 12-month period as a rolling average over a 3-year period for new and new existing MCP and a 5-year period for existing MCP.

(i) for limited operating hours MCPs, there must be an annual assessment of compliance with the rolling average requirements specified in sub-paragraph (h)(ii).

3. Emissions and monitoring

3.1 Emissions to air

3.1.1 There shall be no point source emissions to air except from the applicable sources and emission points listed in Appendix A.

3.1.2 The point source emissions to air shall not exceed the applicable emission limit values given in tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7.

3.1.3 The emission limits for natural gas given in Tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7 can be applied to fuel blends of natural gas and hydrogen, when the relevant percentage multiplier given in Table 3.8 has been applied to them.

Table 3.1 Emission limit value requirements for new MCP or new existing MCP other than engines or gas turbines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	100	35
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	200	100	137	200	200
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	Not applicable	No limit	No limit

Table 3.2 emission limit value requirements for new MCP or new existing MCP which are engines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	40	15
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	190	95	130.2	190	190
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	Not applicable	No limit	No limit

Table 3.3 emission limit value requirements for new MCP or new existing MCP which are gas turbines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	40	15
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	75	50	68.5	75	75
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	Not applicable	No limit	No limit

Table 3.4 emission limit value requirements for all limited operating hours MCP

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	No limit	Not applicable
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	No limit	No limit	No limit	No limit	No limit
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	No limit	No limit	No limit

Table 3.5 emission limit value requirements for existing MCP which are not new existing MCP other than engines or gas turbines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	170	35
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	200	200	274	250	250
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	No limit	No limit	No limit

Table 3.6 emission limit value requirements for existing MCP which are not new existing MCP which are engines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	60	15
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	190	190	260.3	190	190
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	No limit	No limit	No limit

Table 3.7 emission limit value requirements for existing MCP which are not new existing MCP which are gas turbines

Pollutant	Gas oil or gas oil substitutes	Natural gas	Hydrogen	Biogas	Other gaseous fuels
Sulphur dioxide (SO₂) (mg/Nm³)	Not applicable	Not applicable	Not applicable	60	15
Oxides of nitrogen (NO and NO₂ expressed as NO₂) (mg/Nm³)	200	150	205.5	200	200
Carbon monoxide (CO) (mg/Nm³)	No limit	No limit	No limit	No limit	No limit

Table 3.8 Emission limit values for fuel blend of hydrogen with natural gas

Substitution of hydrogen (% v/v)	Pollutant emission limit value expressed as a percentage of the analogous natural gas emission limit value
0 to 20%	100%
Greater than 20% to 50%	107%
Greater than 50% to 75%	115%
Greater than 75% to 90%	125%
Greater than 90% to 95%	130%
Greater than 95% to 100%	137%

3.2 Monitoring

3.2.1 The operator shall, unless otherwise agreed in writing by the Environment Agency, undertake emissions monitoring at each emission point listed in Appendix A for the applicable pollutants specified in tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7.

3.2.2 For new MCP the first monitoring measurements shall be carried out within 4 months of the issue date of the permit or the date when the MCP is first put into operation, whichever is later. For existing MCP the first monitoring measurement shall be taken no later than 4 months after the permit is issued.

3.2.3 Following the first monitoring measurement, monitoring for the applicable pollutants specified in tables 3.1, 3.2, 3.3, 3.5, 3.6 and 3.7 shall be carried out every 3 years.

3.2.4 Following the first monitoring measurement, monitoring for the applicable pollutants specified in table 3.4 shall be carried out once every 1,500 hours of operation with a minimum frequency of once every 5 years.

3.2.5 No monitoring is required for dual fuel boilers during operation on back-up gas oil or gas oil fuel substitutes fuel.

3.2.6 The operator shall, if notified in writing by the Environment Agency, undertake additional monitoring of any MCP for the pollutants specified in tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, and 3.7.

3.2.7 The emissions monitoring shall be carried out in accordance with the guidance ‘monitoring stack emissions: low risk MCPs and specified generators’ or using monitoring equipment, techniques, personnel and organisations with MCERTS certification or MCERTS accreditation (as appropriate), unless otherwise agreed in writing by the Environment Agency.

3.2.8 Monitoring shall not take place during periods of start-up or shutdown.

3.2.9 The operator shall maintain records of all monitoring required by these standard rules including records of the taking and analysis of samples, instrument measurements (periodic and continual), calibrations, examinations, tests and surveys and any assessment or evaluation made on the basis of such data.

4. Information

4.1 Records

4.1.1 All records required to be made by these standard rules shall:

(a) be legible;

(b) be made as soon as reasonably practicable;

(c) if amended, be amended in such a way that the original and any subsequent amendments remain legible, or are capable of retrieval; and be retained, unless otherwise agreed in writing by the Environment Agency, for at least 6 years from the date when the records were made.

4.1.2 The operator shall maintain convenient access, in either electronic or hard copy, to the records, plans and management system required to be maintained by these rules.

4.1.3 The operator shall maintain a record of the type and quantity of fuel used and the total annual hours of operation for each MCP.

4.1.4 The operator shall maintain a record of any events of non-compliance and the measures taken to ensure compliance is restored in the shortest possible time.

4.2 Reporting

4.2.1 The operator shall send all reports and notifications required by these standard rules to the Environment Agency using the contact details supplied in writing by the Environment Agency.

4.2.2 Where monitoring is undertaken in accordance with section 3.2 the operator shall submit to the Environment Agency within 28 days of undertaking the monitoring, using the form made available for the purpose, the information specified on the form relating to that monitoring.

4.2.3 Monitoring results must be converted to standard reference conditions for temperature, pressure and relevant oxygen content, namely the concentration of pollutants in dry air to a temperature of 273.15 K, to a pressure of 101.3 kPa and with an oxygen content of:

(a) 3% for MCPs, other than engines and gas turbines, using liquid and gaseous fuels; and

(b) 15% for engines and gas turbines.

4.3 Notifications

4.3.1 In the event:

(a) of a breach of any of these standard rules the operator must immediately—

   (i) inform the Environment Agency; and

   (ii) take the measures necessary to ensure that compliance is restored within the shortest possible time.

(b) of a breach of any of these standard rules which causes a significant degradation of local air quality, the operator must immediately suspend the operation of the activities or the relevant part of them until compliance with the rules has been restored.

4.3.2 In the event of a breach of rule 2.3.1, operating technique (h)(i) the operator must notify the Environment Agency and include a summary of compliance with the 3 or 5 year rolling average required under rule 2.3.1, operating technique (h)(ii).

4.3.3 Where the operator is notified by the Environment Agency under rule 3.2.6, to undertake monitoring at frequencies not otherwise specified in tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7, the operator shall provide, at least 14 days prior to the monitoring being carried out, details of when the monitoring is to take place.

4.3.4 Any information provided under rules 4.3.1 and 4.3.2 shall be confirmed in writing within 24 hours.

4.3.5 The Environment Agency shall be notified within 14 days of the occurrence of the following matters, except where such disclosure is prohibited by Stock Exchange rules:

Where the operator is a registered company:

(a) any change in the operator’s trading name, registered name or registered office address; and

(b) any steps taken with a view to the operator going into administration, entering into a company voluntary arrangement or being wound up.

Where the operator is a corporate body other than a registered company:

(c) any change in the operator’s name or address; and

(d) any steps taken with a view to the dissolution of the operator.

In any other case:

(e) the death of any of the named operators (where the operator consists of more than one named individual).

(f) any change in the operator’s name(s) or address(es); and any steps taken with a view to the operator, or any one of them, going into bankruptcy, entering into a composition or arrangement with creditors, or, in the case of them being in a partnership, dissolving the partnership.

4.4 Interpretation

4.4.1 In these standard rules the expressions listed under 4.4.1 shall have the meanings given.

‘accident’ means an accident that may result in pollution.

‘activities’ means the operation of the MCP specified in Appendix A.

‘Appendix A’ means Appendix A as attached to the permit.

‘back-up generator’ means a generator used solely for emergency situations such as loss of grid power and not for normal operation, testing beyond the minimum required, or commercial electricity provision.

‘engine’ means a gas engine or liquid fuel engine.

‘EP Regulations’ means The Environmental Permitting (England and Wales) Regulations 2016 SI No.1154 and words and expressions used in these rules or the permit which are also used in the Regulations have the same meanings as in those Regulations.

‘existing MCP’ means MCP with a net rated thermal input equal to or greater than 5MWth and less than 20MWth which was put into operation before 20 December 2018.

‘First put into operation’ means the date when fuel is first combusted in the MCP. This can be during initial on-site commissioning but does not include conformity testing at the place of manufacture of the plant.

‘Gas engine’ means a spark ignition reciprocating engine or compression ignition engine.

‘Gas oil’ is as defined in article 3 (19) of the Directive 2015/2193/EU of the European Parliament and of the Council on the limitation of emissions of certain pollutants into the air from medium combustion plants.

‘Gas oil substitutes’ includes hydrotreated vegetable oil and other liquid fuels approved as being equivalent to gas oil by the Environment Agency, as published in our Medium combustion plant (MCP): comply with emission limit values guidance.‘generator’ means a combustion plant that generates electricity including engines, gas turbines and boilers that operate as combined heat and power.

‘Limited operating hours MCP’ means a new MCP that meets the requirements of paragraph 8 of part 2 of schedule 25A of the EP regulations or an existing MCP which meets the requirements of paragraph 7 of part 2 of schedule 25A of the EP regulations. This includes operators who have signed a declaration that they will not operate the plant for more than 500 hours per year, as a rolling average over 3 years for new MCP and 5 years for existing MCP.

‘liquid fuel engine’ means an internal combustion engine which operates according to the diesel cycle and uses compression ignition to burn fuel. 

‘MCERTS’ means the Environment Agency’s Monitoring Certification Scheme. 

‘MCP’ means medium combustion plant.

‘Monitoring stack emissions, low risk MCPs and specified generators’ refers to the guidance with that title published on GOV.UK and last updated on 12 July 2022, or any subsequent version which makes only editorial changes.

‘new existing MCP’ means an existing MCP specified in Appendix A in respect of which the operator has confirmed that it will comply with the standards applicable to new MCP including but not limited to screening distances to protected habitats and emission limit values.

‘new MCP’ means a MCP with a net rated thermal input equal to or greater than 1MWth and less than 20MWth which was put into operation on or after the 20 December 2018.

‘operating hours’ means the time, expressed in hours, during which a MCP is operating and discharging emissions into the air, excluding start-up and shut-down periods.

‘other gaseous fuels’ means gaseous fuels other than natural gas, biogas and hydrogen

‘primary fuel’ in table 2.2, table 2.3 and table 2.4 means where there is a blend of natural gas and hydrogen the primary fuel is defined as the component that constitutes more than 50% of the blend. If equal, then use natural gas as the primary fuel.

‘protected habitat’ means Special Areas of Conservation (SAC), Special Protection Areas (SPA), Ramsar Sites, Marine Conservation Zones (MCZ) and Sites of Special Scientific Interest (SSSI).

‘Relevant Air Quality Plan’ means an air quality plan enacted through the Air Quality Standards Regulations 2010, Part 5, Paragraph 26

‘year’ means calendar year ending 31 December.

4.4.2 In these standard rules:

(a) references to reports and notifications mean written reports and notifications, except where reference is made to notification being made immediately, in which case it may be provided by telephone.

(b) references to pollutant emission limit values set out in tables 3.1, 3.2, 3.3, 3.4, 3.5, 3.6 and 3.7 are expressed at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases and at a standardised O₂ content of 3% for medium combustion plants, other than engines and gas turbines, using liquid and gaseous fuels and 15% for engines and gas turbines.

End of standard rules.

Record of changes

Version	Date	Change
1.0	April 2018	Published for SRP consultation May 2018.
1.0	August 2018	Published for use August 2018.
2.0	July 2019	Published for consultation on amendments.
2.0	July 2019	Published for use July 2019.
2.1	January 2020	Insertion of the word ‘testing’ into the text in table 2.2 relating to an engine operating as a back-up generator.
2.2 Draft	October 2022	Revision to allow existing MCP greater than 5 MWth to less than 20MWth.
2.3	March 2023	Revision following a consultation on 2.2 draft.
2.4	February 2026	Revision following consultation on addition of gas oil substitutes and hydrogen as a fuel and restrictions on vertical stacks, caps and cowls.