OK I will accept the word of your eletrician that it should be bonded (is an extraneous-conductive-part) because they should know.
Not all pipework is needed to be bonded unless less it is. That might sound strange to some.
If bonding is needed it is safer to have it, if it is not needed it is potentially safer to not have it.
If it is not exactly clear whether it is or is not, plus if that is deemed likely to change from needed to not needed throughout say the seasons or because of likely changing conditions then a judgement call has to be made.
Having said all of that I would usually bond anyway even if I deem it not strictly absolutely nessacary at most times and I would be inclined to consider changing readings over time intervals.
Generally that is the safer option but not always and in some circumstances it could be safer not to bond.
I just wante to see that you had taken reasonable steps to ascertain that and blindly followed any myths. By asking someone who should know so well done you.
Well that is my opinion and there may be other opinions.
As one famous contributor used to say "Everbody is entitled to my opinion"
As an aside, although I have retired I did take charge recently of works by others and I verified visually and by proper testgear readings that the incomming gas supply was not an extraneous-conductiv-part yet there was a boiler there with an earth supply which would make it earthy and the water supply was temporary but the likelihood was that it would become earthy in the near future one a permanent supply was done so I decided that all considered the gas supply was very likely to need the main bonding in the very near future and decided that it should be main bonded and leave it to a future electrician to decide if they wanted to disconnect it.
I do not think there was any other option I could reasonably do!
