Anyway ask Transco to run there sniffer over it. It does seem a bit of an unusual way of doing things to me. If you report a leak, Transco usually test your gas carcass and if a drop is found they shut and cap it off or tell you to get a Gas Safe guy in to find where the leak is.
I had a problem with one where I moved a gas pipe in the kitchen, tested before I went home, everything was fine. The next the sparky was in re-wiring the kitchen, took the floor up and could smell gas, so the foreman rang me, could I go and have a look whilst I was in the same street, went around put a drop test on and it was fine, but there was defernitly a smell of gas, and my sniffer was picking it up.
The foreman came around and asked if I found anything, I told the u gauge had been on half an hour and probably dropped 1mb.
We had a look around and could not find anything until I realised, that was timber framed house and on the back of the kitchen was next doors kitchen, so I suggested the leak was coming from there, and the foreman agreed and we called transco. The next door void property which we could not get access.
Transco came out with there £1500 sniffer and said they could not detect any trace off gas.
Two weeks later, the goes into the void property, and theres a strong smell of gas coming from the cooker hose. God knows how long that was leaking, and could you imagine the consequences if that went up