Weights and measures: Legal Metrology Delivery

Information for businesses.

The Office for Product Safety and Standards (OPSS) is a world leader in Legal Metrology: the application of legal requirements to measurements and measuring instruments. It supports local government through its purpose-built laboratories in Teddington and upholds its statutory duties. Its specialised services are offered through its Legal Metrology Delivery (LMD) team.

Our services

LMD provides statutory calibration under the Weights and Measures Act 1985 and the Coinage Act 1971 on behalf of the Secretary of State. It checks the accuracy of the mass, length and volume local standards held by local authorities and the UK’s coin standards for the Royal Mint. It also holds the trial plates for the hallmarking assay offices.

Read about our calibration service

Within the UK, the legal framework for conformity assessment is underpinned by the Measuring Instruments (MI) Regulations 2016 and the Non-Automatic Weighing Instruments (NAWI) Regulations 2016 (both as amended). On 30 April 2022, OPSS withdrew from the commercial conformity assessment market, where it operated under the NMO brand. LMD can however still issue certifications in relation to other UK regulations under Section 12 of the Weights and Measures Act 1985 – where alternative national provision is unavailable.

Read about our product certification service

Read about our pre-assessment service

Outside the UK, the International Organisation of Legal Metrology (OIML) produces recommendations for specific weighing and measuring instruments. OPSS is an Issuing Authority under the OIML Certification System. This certification can avoid the duplication of tests when applying for national or regional certification outside the UK.

Read about OIML certification – OIML website

The equipment in the laboratories at our Teddington site is fully traceable to national standards and operated in accordance with ISO/IEC 17025:2017.

Read about our testing facilities

OPSS is committed to achieving certification of its approach to managing the hazards relating to its laboratory-based activities through the British Standard for Occupational Health and Safety BS ISO 45001:2018.

Certificates issued by OPSS

OPSS publishes any certificates it issues under national legislation.

Access the lists of UK national certificates

Until 30 April 2022, OPSS also published NMO branded certificates on GOV.UK issued under the MI and NAWI Regulations or for EEC type examination. These certificates are no longer updated by OPSS. Accordingly, the legacy GOV.UK pages on which they were presented were unpublished on 20 July 2022. NMO branded certificates issued up to 30 April 2022 remain available for reference and as a matter of public record on the National Archives.

Access the legacy NMO MI certificates – National Archive website

Access the legacy NMO NAWI certificates – National Archive website

Access the legacy NMO EEC certificates – National Archive website


Should you wish to make a complaint about the services we provide:

Read the OPSS complaints procedure


  • explain your complaint and any related issues
  • provide examples or supporting evidence where possible
  • describe the action you would like us to take to resolve matters

Process overview

  1. Acknowledgement – All complaints will be acknowledged within 5 working days, but we aim to acknowledge them immediately.
  2. Investigation – The Quality Manager will ensure a full investigation is carried out, the level of which will be commensurate with the frequency of occurrence and severity of the complaint.
  3. Response – Once the investigation has concluded, we will address the complaint by taking the necessary action.
  4. Communication – The decision in relation to the complaint will be documented, recorded, and sent to the complainant within 20 working days from the acknowledgment of the complaint.


Should you wish to appeal against a technical or certification decision we have made, you can do so under the OPSS complaints procedure.

Appeals may be made, for example, against our decisions to refuse or suspend certification.

Your appeal will be acknowledged within 5 working days. If deemed valid, it will be reviewed and a decision communicated to you within 20 working days from the acknowledgment of your appeal. A robust explanation for our decision will be included.

Contact LMD

For local authority enquiries please email

For all other enquiries please email

Write to:

Legal Metrology Delivery
Office for Product Safety and Standards
Stanton Avenue
TW11 0JZ

Published 20 July 2022