Construction and installation
Hi
The supply you have is polyethylene within a sleeve is designed purely for external use. The only time plastic can be used within a premise is if it is inserted into a carrier pipe (old steel gas pipe) and the annulus sealed with a fore proof sealant. The service pipe within the building shouod therefore be steel and there should be no buried joints. The breach is actually of the Pipeline safety Regs 1996.
These regs govern materials and construction of pipelines. Here is an extract which wil help explain:
9. The operator shall ensure that no fluid is conveyed in a pipeline (save for the purpose of testing it) unless it has been so constructed and installed that, so far as is reasonably practicable, it is sound and fit for the purpose for which it has been designed.
As your pipe is now inside it is no longer deemed fit for purpose. The gas companies have internal procedures to comply with PSR96 namely MSL1. This document has a section on built over services.
the work can be charged to you or your gas supply isolated on dafety grounds, however if a previous owner built the extension then under the Gas Act you cannot be charged.