GB pretended :
Surely, he did a pressure drop test?

That I don't know - I wasn't living there and was working away. It was
a chromed copper pipe 'soldered' into an elbow, where the chrome had
not been removed by the BG engineer. As anyone with any experience will
know, you cannot solder onto chrome.

I had smelled a slight smell of gas every time I had been there, put
put it down to the new water heater. One day when I visited it was
particularly strong, so I investigated and found the pipe loose in the
solder elbow with signs that it had been attempted to be soldered. One
accidental kick and it would have been completely out. I isolated the
gas and called the GB out on an emergency.

It might well have passed a pressure test when first installed, but
like many jobs it relies on work being done with competence.