Joe the short answer is; No!

And now for the long answer: 'The Proof Acts lay down that no small arms may be sold, exchanged or exported, exposed or kept for sale or exchange or pawned unless and until it has been fully proved and duly marked. The maximum penalty is £1,000 for each offence, but with provision for higher penalties where, for instance, the sale of a number of guns constitutes one offence.'

That was taken from the Notes on the Proof of Shotguns & Other Small Arms issued by the Birmingham Proof House. The last edition I have is from 1992 so the penalty might have gone up since then. Lagopus…..