when carrying out work on gas the first job is to carry out a gas tightness check at the test nipple on the customers side of the meter to see if the system leaks or is gas tight.
gas workers are trained from this basic step.it is supposed to be carried out before and after (to show you have,nt left a leak) ,but most gas workers test any disturbed joints they touched with leak detection fluid/aerosol on the grounds they test what they touched and sod putting anyone else,s work right, well time is money.
if a leak is discovered they are obliged to locate and repair the leak, quite easy to establish if its an appliance or the gas carcase. after the first test disconnect all the appliances and test again.if leak continues its in the carcase(more later).if no leak in second test then an appliance is suspected so reconnect one by one untill leak occurs again and fix.
if the leak is suspected in the carcase(all gas pipe runs starting at meter) then each joint needs to be tested with LDF untill a leak (s) is/are found.this is the hard part potentially as most of the carcase is buried, mostly under floorboards and can become costly
i do symphatise with your problem but if a leak has been found/proved then it needs to be repaired.ask BG to explain how it was found
ps more bad news ,certain leaks are considered acceptable on older carcases with certain meters, just to complicate things
sorry for the long answer but not an easy question