to OP spot on. i work for BG as a meter engineer and in the course of my work have to check all gas appliances, you would not believe the amount of installations i have to cap off due to dodgy landlords, stupid tennants etc, i
since i started there have been 2 serious gas explosion incidents whereby houses have been demolished,
for me working london its astonishing how blase peeps are with regards to gas.
atho qualified to work meters and pipe work including medium pressure and upto 6"pipe i would not dream of attempting to fix a boiler, in no way just because im gas safe does it entitle me to work on anything!