Sealing disk at the gas meter would be a good one. Non destructive and easily reversed.
i have done this twas about five year ago , done a repair on a baxi pump had gone ping invoiced the cust (knew him through a mate) never got paid .
He claimed boiler still never worked so wasn't paying even tho i found out he was lying (same mate told me)
Waited a few weeks then went out disc in meter , my friend told me he was furious as he called out another engineer who charged him to take a disc out lol