I suspect George Blake, the MI6 officer turned KGB double agent, would enjoy toddling over to the Hampstead Theatre to see himself in the new production of Simon Gray’s play Cell Mates. The problem is that the instant he landed at Heathrow, he’d be arrested and made to serve the remaining 37 years of his 42-year jail sentence, which was rudely interrupted by his escape from Wormwood Scrubs in 1966.