In-service testing for gas and electricity meters
Source: gov.uk (2025-11-06)

IST is a national sampling scheme based on the British Standard BS 6002-1:1993 (sampling procedures for inspection by variables).

What is IST?

In-service testing (IST) is a national sampling scheme for gas and electricity meters based on the British Standard BS 6002-1:1993 (sampling procedures for inspection by variables).

The Office for Product Safety and Standards (OPSS) contacts suppliers on a yearly basis to request information about the meters in their portfolios, including manufacturer, model number, year of installation, and population size. OPSS then collates this information to obtain a list of meter samples required for IST. The sample sizes are allocated in proportion to the overall population size as detailed in the IST handbook and the British Standard.

Suppliers are requested to submit the required number of samples to approved IST test stations for laboratory testing. Finally, OPSS collates the test results and assesses the performance of individual meter populations using the agreed criteria.

IST takes place at regular intervals throughout the lifespan of a gas or electricity meter. Meters may continue in-service for as long as they conform to the regulations, while meters that no longer conform need to be removed from service. IST therefore forms an important part of consumer protection by ensuring only meters that operate within the prescribed limits of accuracy are used for consumer billing.

Scope of IST

The IST methodology was developed for domestic type meters approved under the Measuring Instruments Directive 2014 (MID). Domestic type meters are defined as those with a maximum capacity of 6 cubic metres per hour (gas) and whole current meters (electricity).

OPSS has also extended the IST methodology to electricity meters approved under GB legislation prior to MID coming into force. IST can assist suppliers to manage their meter portfolios during the transition to ‘smart meters’.

Read guidance on approved gas and electricity meters. (https://www.gov.uk/guidance/approved-gas-and-electricity-meters)

In future it may be possible to extend the IST methodology to cover non-domestic meters (for instance, larger meters installed in industrial and commercial premises). However, the statistical process detailed in the IST handbook will need to be modified to account for the much smaller populations of these meters.

Implementation

OPSS has established a further expert group (IST4) to implement the IST scheme. This group is open to all interested parties including energy suppliers, asset owners, trade organisations and meters manufacturers.

IST reports

The Industry Metering Advisory Group (IMAG), sponsored by ELEXON (http://www.elexon.co.uk/) and Ofgem (https://www.ofgem.gov.uk/), set up the IST and Post-MID expert group (IST1), to develop proposals for the in-service accuracy monitoring of MID approved domestic type gas and electricity meters. A further expert group (IST2) was subsequently established to develop additional proposals to ensure the other legislative requirements aside from meter accuracy were also covered.

The combined proposals of these groups were published in the IST group 1 and 2 report that was accepted by IMAG and Ofgem in 2008. These proposals set out a methodology based on sample testing whereby energy suppliers and asset owners can demonstrate they are fulfilling their statutory obligation to keep their meter populations in proper order for correctly registering the quantities of gas and electricity consumed.

Read the IST group 1 and 2 report. (https://www.gov.uk/government/publications/in-service-testing-group-1-and-2-report)

A further expert group (IST3) was then established to consider the costs of the IST scheme and possible governance arrangements. Its findings were published in the IST group 3 report in 2009. A joint consultation on the governance options was subsequently published.

Read the IST group 3 report. (https://www.gov.uk/government/publications/in-service-testing-group-3-report)

IST handbook

The IST handbook is a culmination of the IST group 1/2 and the IST group 3 reports. It is designed to provide stakeholders undertaking sample testing with an understanding of the sampling methodology, test processes, assessment methods and final assessment criteria. The handbook includes details of IST test stations that have been approved by OPSS for the in-service testing of gas and electricity meters.

Read the IST handbook. (https://www.gov.uk/government/publications/in-service-testing-handbook-for-gas-and-electricity-meters)

The handbook is a working document and amendments will be made when necessary as the implementation of IST develops over time.

Templates for gas and electricity meters tested

OPSS approved IST test stations and suppliers / submitters can use OPSS templates if they wish to submit IST results. To get the appropriate template, please email the relevant team using the contact details below, specifying the gas or electricity meter type to be tested. ##Contact

If you wish to speak to a member of staff please contact:

Email:

xxx@xxx.xx (mailto:xxx@xxx.xx)

xxx@xxx.xx (mailto:xxx@xxx.xx)

Gas and electricity metering team: In-service testingOffice for Product Safety and StandardsStanton AvenueTeddingtonMiddlesexTW11 0JZ

Reception: xx-xxxx-xxxx