I beg to differ, with older meters and cutouts it was rarely contended as it was actually hard to prove unless you admitted it and it was recorded, with modern smart meters now there has been cases where the DNO has submitted a fine normally to the home owner due to the meters been powered down in conjunction with missing meter seals... I know because it happened to a mate, he didn't like the quote from his energy supplier to drop the tails out so he got a sparky mate to do it (not me) and upgrade the board too, because he enquired about a cost and because the smart meter registered a power down while no network issues were present he got a knock on the door and they inspected his meter... he was asked to provide the Electricians details but refused as it was his friend .. he as the house owner was subsequently handed a hefty fine.... it does happen but only when they have enough evidence to proceed and issue a fine.
Smart meters now log times and dates of any power outs, that is half the evidence they need the rest just needs the correct circumstances for them to suspect it has been done, in my mates case he rang for a quote, had he not got a mate in I would suspect he would have passed on the details and shown them an invoice for work done..