Measuring Instruments Directive

The following summary is quoted from the  MID Guide published by SHM Communications 

Any meter used for billing of electricity, must be either MID approved or approved under UK National legislation. Meters already installed, that were approved under UK National legislation prior to October 2006 may remain installed indefinitely, as long as they are measuring accurately. Any new meter manufactured and approved after October 2006 must be approved under the MID regulations.

In the UK, the MID is applicable for loads up to 100kW. After October 2016 every new meter installed for billing must be MID approved. It is a criminal offence to use a non approved meter for billing. MID makes no distinction between primary main supply meters and secondary sub-billing meters. They are ALL billing meters.