Thanks Damo, noseall and Bernard for your comments - very helpful.
Sounds like it should be possible to get the extension shell in place with a new meter position, before National Grid come and do the repositioning of the pipe and meter. We have a well recommended builder lined up, so are...
My biggest worry is that the foundations/new floor pad of the new side extension are going to have to negotiate the existing supply pipe that runs up the drive under the concrete. It only emerges immediately below where it runs up the wall before entering the house. The gas pipeline companies...
We are planning a single storey rear and side extension to our smallish semi house.
The gas supply currently enters the house above ground and dpc through the external side wall into the under stair cupboard, which is where the gas and electric meters + electric fuse box have all been since...