Consultation outcome

Amendments to standard rules permits for medium combustion plant and specified generators: summary of consultation responses

Updated 19 January 2026

1. Introduction

The purpose of the consultation was to get feedback on a proposed set of changes to standard rules permits (SRPs) associated with the ongoing implementation of the Medium Combustion Plant Directive (MCPD) EU/2015/2193. 

This document summarises the responses we received and explains how we have considered and addressed the feedback and what we will do next.

2. How we ran the consultation

We ran the consultation for 8 weeks from 15 September 2025 to 9 November 2025. It was hosted on Citizen Space, our online consultation platform. It was open to all stakeholders with an interest in medium combustion plant (MCP) and specified generators (SGs) and their emissions to air.

The consultation was run in line with our legal requirements to consult following the Cabinet Office’s consultation principles guidelines.

We promoted the consultation through direct engagement with industry stakeholders, including operators, trade associations, and public sector bodies. We also shared information through our existing networks and published details on GOV.UK to encourage broad participation.

Respondents were invited to provide feedback on the proposed changes to MCP and SG SRPs. Responses could be made by using the online consultation tool or by submitting a completed response form by email.

All responses received within the consultation period were reviewed and analysed. This document summarises the feedback and explains what we have decided to do next.

We received 10 responses in total from:

• 6 operators
• 2 trade bodies
• 1 member of the public
• 1 consultancy

3. Summary of key findings and actions we will take

3.1 Proposed changes to standard rules 2018 No 4

We proposed to amend Table 3.2 of SR2018 No 4 to correct what we believed was an error. Specifically, we stated that the emission limit value (ELV) for oxides of nitrogen (NO and NO₂ expressed as NO₂) for gas engines which are new MCP should be 95mg/Nm³, which we thought was in line with the requirements of the MCPD.

After reviewing the feedback and the MCPD requirements, we acknowledge that our initial proposal was incorrect.

The permit in question is for an SG operating less than 500 hours per year. While these generators are also new MCP, the MCP rules apply only above 500 hours per year of operation. Therefore, the exemption remains valid, and the stricter limit of 95 milligrams per normal cubic metre (mg/Nm³) does not apply to these low-use generators. The correct limit for generators operating under 500 hours per year remains 190mg/Nm³, consistent with Article 6(8) of the MCPD and Schedule 25B of the environmental permitting regulations (EPR).

3.2 Proposed changes to standard rules 2018 No 2 and 3

We proposed to amend SR2018 No 3 Table 2.3 by removing operating technique (e). Our reasoning was that the current wording implied compliance with NOx ELVs within 10 or 20 minutes, which aligns with tranche A and B generators under Schedule 25B of EPR. However, the ELVs in this rule set are stricter than those in Schedule 25B, creating potential inconsistency.

One respondent agreed that the change would prevent misinterpretation, breaches of permit conditions, and potential environmental harm and that clear compliance timescales help maintain alignment with SG regulations and avoid ambiguity.

Another respondent said that removing the 10- and 20-minute compliance timescales could undermine regulatory consistency. Also that while these timescales currently apply to the 190mg/Nm³ NOx limit for SGs, they could also be relevant for tighter ELVs.

There was also a suggestion that if current timescales are impractical for certain abatement technologies, a revised, technology-appropriate timeframe should be considered.

After considering feedback, we will amend Table 2.3 by replacing operating technique (e) with ‘Any abatement plant should be designed and operated to achieve compliance with the ELV in Table 2.3 in the shortest possible time’.

We think this is proportionate as plant operating under a SR2018 No 3 permit are unlikely to involve multiple start-ups, so the risk is low. This wording balances concerns about impractical compliance timescales while maintaining environmental protection. It places responsibility on operators to achieve compliance as quickly as possible without imposing rigid timeframes that may not suit all technologies.

We also proposed withdrawing these standard rules sets for new applications from 28 February 2026 due to low uptake.

There was mixed feedback with some respondents agreeing that these SRPs apply in very few cases and that alternative permits can cover the same activities.

However, several respondents opposed withdrawal unless there had been no uptake or the SRPs were being superseded or consolidated. Even with low uptake, SRPs were seen as offering significant cost and efficiency benefits for both applicants and regulators compared to bespoke permits. Their continued availability supports streamlined permitting for low-risk, well-understood activities.

After reviewing feedback, we have decided to withdraw these rules sets for new applicants or plant from the 28 February 2026.

This is justified on the basis that there have been no applications made for these rules sets since 2023, and no evidence was provided by respondents to suggest future demand for these SRPs. In addition, other feedback outside of the consultation has indicated confusion among operators about differences between the various SG SRPs. We therefore believe reducing the options will ensure clearer differentiation between the remaining rules sets. We are however committed to developing new SG standard rules sets with a broader scope, like MCP SR2018 No 7 for MCPs, to cover more potential SG operations. We welcome suggestions from stakeholders as to what types of low-risk SG operations we should consider.

3.3 Proposed removal of standard rules 2018 No 5, 6, 8 and 9

We proposed that, due to very low uptake, these SRPs should no longer be available to new or existing holders from 28 February 2026. Removing them will reduce the burden on the Environment Agency to maintain rules sets and allow us to focus our regulatory effort on creating standard rules for other low-risk activities in this sector.

Feedback indicated that these rule sets have low relevance and uptake because most new SGs are over 1 megawatts thermal (MWth) and used for grid export, while plants under 1MWth typically operate in island mode and are exempt from MCPD and SG regulations. Respondents noted that other SRPs could easily cover the same criteria with minimal updates.

However, others raised concerns about clarity for existing holders and potential costs or resource burdens when varying to other permit types. A few respondents argued that even with low uptake, SRPs offer cost and efficiency benefits over bespoke permits and should therefore be retained. Respondents cautioned that efficiency gains for the Environment Agency should not compromise proportionate and accessible compliance routes for industry.

Having considered the feedback, we will proceed with withdrawing all these rules sets for both new and existing customers. Our records show that one operator currently holds a permit for SR2018 No 5 and 2 operators hold permits for SR2018 No 9. There are no permit holders for the other rules sets. We will work with affected operators to vary their permits to a simple bespoke permit, free of charge. The ELV and monitoring requirements will remain the same as in their SRP, and subsistence charges will also remain unchanged.

For SR2018 No 8, we are planning a separate consultation in 2026 on our new approach to permitting mobile MCPs, which will include a proposed replacement standard rules set.

We are also committed to developing new SG standard rules set with a broader scope, like MCP SR2018 No 7, to cover more potential operations and therefore offer a proportionate and accessible route to permit compliance for operators. We welcome suggestions from stakeholders as to what we should include in addition to those already provided in this consultation. This approach will simplify choices for operators and ensure clearer differentiation between rules sets.

3.4 New proposals for standard rules

We asked if there were other MCP and SG activities which you thought might benefit from a low-risk standard rules set in the future which we could consider developing.

In the responses there was support for developing new SRPs for low-risk biomass boilers (<2 MWth) using virgin biomass. The respondent felt that screening tools like Simple Calculation of Atmospheric Impact Limits (SCAIL) and air quality assessment show minimal environmental impact when receptors are over 2km away, suggesting bespoke permits may be unnecessary in such cases.

The remainder of the responses focused on how standard rules support reduced administrative burden for operators and allow the Environment Agency to focus on higher-risk sites. Respondents also felt that SRPs support UK energy security and decarbonisation goals.

There were also concerns raised over the inconsistent permitting requirements for low-risk combustion plant on IED sites versus standalone combustion plant. Feedback was that SRPs already include safeguards (for example stack height, receptor screening, operating techniques) that could be considered best available techniques (BAT). It was suggested that applying SRPs to IED sites could simplify permit variations and reduce regulatory burden.

Some respondents suggested that a registration-based approach (as proposed for MCPs from 2029 in a recent Department for Environment, Food & Rural Affairs (Defra) EPR regulation reform consultation) may be simpler and equally effective compared to introducing new SRPs.

Having reviewed this feedback we will look at creating an SRP for low-risk biomass boilers using virgin biomass ahead of the requirement for this type of plant to have a permit in January 2029.

We are awaiting Defra’s consultation response about registration as an alternative to permitting for MCP and SG. We will be led by them as the policy decision maker.

SRPs can be permitted on installations only where the activity is not a directly associated activity. This is because the IED requires activities on an installation to be subject to wider environmental controls than those under MCPD and SG rules. We ask respondents to refer to regulatory guidance note (RGN) 2 for a fuller explanation of this position.

We are however satisfied that operators may use screening tools such as SCAIL, provided these activities are not part of a 1.1 combustion activity. We have updated our guidance medium combustion plant: screening tool and specified generator: apply for an environmental permit to reflect this position.

3.5 Hydrogen as a fuel on standard rules 2018 No 7 and 2022 No 9

We are proposing to expand the range of fuels which can be combusted within these standard rules sets to include hydrogen.

We proposed that the ELVs for the combustion of hydrogen would align with our guidance for hydrogen ELVs. We will also set an appropriate screening distance to habitats for this fuel type. The introduction of hydrogen as a fuel within this rules set will provide a viable route to decarbonisation for this type of plant. 

Respondents strongly support the inclusion of hydrogen as a fuel in SRPs, citing its growing availability, reduced cost, and ease of retrofitting existing engines. Hydrogen combustion is seen as low-risk and environmentally positive. Including it in SRPs aligns with UK decarbonisation goals and net zero commitments. It simplifies the regulatory process and reduces administrative burden for operators switching from diesel to cleaner fuels. The proposal was viewed by some respondents as future-focused and proportionate, helping to foster innovation and support the transition to low-carbon technologies.

Following a review of the feedback we have decided to proceed towards adding hydrogen into all remaining MCP and SG SRPs which currently allow the use of natural gas as a fuel. That includes SR2018 No 1, SR2018 No 4, SR2018 No 7 and SR2022 No 9.

Although not an MCP or SG activity, one respondent also supported developing a separate SRP for hydrogen production by electrolysis, due to its minimal environmental impact and recognition in updated IED thresholds.

Defra have recently consulted on simplified approaches for regulation of hydrogen production via electrolysis as part of its Consultation on modernising environmental permitting for industry. In parallel, the Environment Agency is working on developing the option of an SRP for hydrogen production via electrolysis.

3.6 Gas oil substitutes on standard rules 2018 No 7

We are proposing to expand the range of fuels which can be combusted within this rules set to include gas oil substitutes (for example hydrotreated vegetable oil – HVO).

We recognise that there are several alternative liquid fuels which can act as a substitute to gas oil on the market which operators wish to combust in their MCP. The Environment Agency has recently published a regulatory position statement Using drop-in fuels in combustion plant instead of gas oil: RPS 337 which sets out the conditions and types of fuel we will allow under the description of ‘gas oil substitutes’. Currently, this only includes HVO but will remain under review should other fuels be considered. We propose to add ‘gas oil substitute’ as a fuel type within this rules set with the same ELVs and distances to habitats as ‘gas oil’.

We will also add an interpretation for ‘gas oil substitute’ setting out that the use of this fuel has been agreed in writing with the Environment Agency and where in the guidance we will maintain a list of fuels which sit within this interpretation.

Respondents widely support the inclusion of HVO as a fuel in SR2018 No 7, citing its environmental benefits and operational reliability.

For example, a respondent said that HVO offers lower NOx and CO₂ emissions compared to diesel. Its use supports decarbonisation and aligns with UK net zero goals. Including HVO in SRPs would reduce the administrative burden and simplify fuel switching for operators.

The proposal is seen as practical, proportionate, and future-focused, helping operators adopt cleaner fuels more easily and encouraging innovation in the sector. And that inclusion of HVO supports both national environmental policies and individual organisational sustainability goals.

In response to this feedback, we will proceed towards adding gas oil substitutes (for example HVO) to SR2018 No 7 and SR2018 No 4 and as a back up fuel on SR2022 No 9.

3.7 Horizontal stacks, caps and cowls

We are at looking at the option of removing the restriction on caps and cowls and horizontal stacks on standard rules permit SR2018 No 7 and SR2022 No 9. The intention is to increase the number of operations which can apply for this rules set in particular existing backup generators due to be permitted by 2029 under the current requirements of EPR. This may result in us needing to set relevant screening distances to consider the potential impact to air dispersion for this type of stack configuration. 

We asked stakeholders if they had any views on the removal of the restrictions on caps and cowls and horizontal stacks in SR2018 No 7 and SR2022 No 9.

The responses included comments that most plants are now installed vertically without caps or cowls, reflecting current industry practice. However, there was also strong support for removing the restrictions on stack configurations with some feeling that these features are common in existing installations and often necessary to prevent water ingress and maintain operational reliability.

One respondent said that for low-use generators (for example <50 hours per year), especially backup and emergency units, the environmental impact of horizontal stacks is considered negligible. Removing restrictions would not significantly affect air dispersion or ecological receptors.

We also received feedback that said that removing these restrictions would avoid costly redesigns or retrofits and prevents unnecessary defaulting to bespoke permits, which increases administrative burden for both operators and the Environment Agency.

The position would also support operational flexibility and resilience.

Water and glass manufacturing sectors highlighted the impracticality and cost of retrofitting large numbers of generators.

Respondents noted that most plants already meet performance standards regardless of stack orientation.

Respondents had suggestions for implementation such as retaining current screening distances for vertical and unimpeded stacks. Introduce separate criteria for horizontal or impeded stacks to maintain clarity and proportionality and consideration of a registration scheme for small, emergency-use MCPs in low-sensitivity areas.

Some respondents requested further guidance on how the change might affect air dispersion modelling and compliance with air quality standards.

After reviewing the feedback we have decided to amend operating technique 2.3.1 (d) on SR2018 No 7 and SR2022 No 9 allowing operators some flexibility with regards to their stack configurability if needed. For example plant which is an emergency back-up and a different stack configuration is required to prevent the ingress of water through low usage. We still recommend that vertical stacks without caps and cowls is best practice and should be deployed wherever possible. The screening distances in the standard rules sets will remain the same regardless of this change.

4. Next steps

We will consider these consultation responses when we further develop the remaining rules sets and in the potential creation of new SRPs.

We will withdraw rules sets 2018 No 2, 3, 5, 6, 8 and 9 for new applicants before the 28 February 2026. In the case of operators currently holding an SRP for SR2018 No 5 and 9 we will contact these operators in January 2026 to set out the timescales and process for transferring them onto a simple bespoke permit instead. Once this is complete, we will fully withdraw these rules sets for existing operators. 

We aim to amend SRPs with revisions relating to hydrogen, gas oil substitutes and horizontal stacks or caps and cowls in the next 6 months.

If you want to discuss your consultation response or the points made within this document please email combustion@environment-agency.gov.uk.

5. List of respondents

• NFU Energy Ltd
• Northampton General Hospital NHS Trust
• British Glass – trade association which represents the manufacturers of container glass, flat glass and glass wool insulation
• Southern Water Services Limited
• United Utilities
• E.ON UK
• Thames Water Utilities Limited
• Joint Environmental Programme – co-funded programme of research into the environmental impacts of electricity generation jointly funded by Drax Power, EPUKi, RWE, SSE Thermal, Uniper, VPI and WBE
• SSE