Spot on Peter, pointless indeed, but the law is the law and we have to follow it to the letter unfortunately, we have all seen milsurps that are not in (legal) proof on the range.
By way of example, a certain large UKdealer sold a friend of mine an Enfield last year, he was very pleased with it and brought it round for some advice regarding changing the furniture, on inspection, no civvy proof. As he is quite new to shooting I spoke to them on his behalf, confident that this rifle had just slipped through by mistake and it could all be taken care of ... Not a bit of it, I was "told" by the rather snotty owner that military proof marks are adequate and that I had no idea what I was talking about ...
I suggested he might want to read up and call me back, he did, apologised and the rifle was collected proofed and returned. But how many had he sold prior to this, if something goes wrong and there is an accident with one (god forbid) he will be hung out to dry by the Police and his business insurance ... broke and banged up for the sake of a £50 proof!
The flip side of the coin, if you are shooting said rifle and its goes "bang" and injures your neighbour in the next shooting point, your shooting insurance will be invalid and quite possibly your FAC, as you aren't following the set conditions.