Is it not the case that even if the incoming gas is fed in plastic, that the actual internal gas pipework being metallic does require bonding still. I seem to recall reading that in the regs approx 4 years or so ago. If I recall correctly it applied specifically to gas but not to all metallic water pipework (even when the incoming water was plastic too).
The requirement is to bond extraneous conductive-parts.
Plastic is non-conductive, so doesn’t require bonding.
Metallic pipework inside the building is not extraneous, so also doesn’t require bonding.
When you look up the definition of extraneous conductive-part, it says something about not being a part of the electrical installation which may introduce a potential (might be introduce a difference in potential).
Determination of whether the pipework introduces a potential (or a difference in potential) would indicate whether it requires bonding.
I’m pretty certain this has been covered a number of times.
Use an IR tester to determine whether there is any continuity between the installation earth and the pipework and use a low ohm meter to determine whether any continuity found is reliable.
Below 0.05 ohms is considered reliably connected and doesn’t require bonding.
Anything between 0.05 ohms and 23 kohms would be considered as being in contact with earth, though there are different opinions regarding the higher end as to whether it would require bonding.
22k ohms, 1667 ohms or 667 ohms, all dependant on the resistance of an average human body (1 kohm) and the 50v considered as being safe.