Surely there is a standard procedure for this type of thing?
In the same way that an electrician will 'earth spike' a power cable to see if it's live will not a gas man perhaps drill a small hole to test for pressure and have a threaded plug ready to plug the hole if it turns out to be live?
I'm not suggesting that is the right thing to do in this case but it may be what I might suggest having tried to trace the pipework back or confirmed that pipes from the meter only go to one or two newer appliances.
Seems strange to me that the gas industry doesn't have a standaed procedure for this type of investigation.
In the same way that an electrician will 'earth spike' a power cable to see if it's live will not a gas man perhaps drill a small hole to test for pressure and have a threaded plug ready to plug the hole if it turns out to be live?
I'm not suggesting that is the right thing to do in this case but it may be what I might suggest having tried to trace the pipework back or confirmed that pipes from the meter only go to one or two newer appliances.
Seems strange to me that the gas industry doesn't have a standaed procedure for this type of investigation.