Hi - I work at National Grid and spotted this post. I chased this up with my colleague Mark Balmega in National Grid Metering and he sent this response:
I am responsible for Operational Delivery for for National Grid Metering. I have read your forum post and I would just like to respond in an attempt to clarify some of your concerns. Each year, National Grid carries out an extensive policy meter replacement programme of around 100,000 meters across Britain. This is called the Policy Meter Exchange programme and National Grid has an obligation to do this. This is so that National Grid can ensure the meters are operating safely and accurately.
Policy Meter Exchange (PME) Obligation
National Grid's licence to operate includes an obligation for meter installations to be periodically checked for safety and accuracy. Once identified, meters requiring "policy" maintenance are usually exchanged for a newer model and this has been approved by the Gas Regulator, Ofgem. It is not our intention to cause our customers inconvenience.
There is no charge for any work carried out under the programme. However, National Grid has a responsibility to notify end consumers of any potential safety issues that may be identified during the meter exchange.
If you require any further information relating to this matter, please do not hesitate to contact National Grid on 0845 606 6766.
Hope that is helpful.