Final (?) edit: I was contacted by someone who said he knew the t-shirt wearer and that it was, in fact, real – the gentleman in question is a union official with a speech defect resulting from an operation (this fits with reports I’ve read that the man in the shirt had difficulty speaking).
The message on the t-shirt was intended as a tongue-in-cheek reference to Nye Bevan’s famour ‘Tories are lower than vermin’ speech, which the wearer realises backfired and now regrets.
Unless and until someone refutes this account, which appears to be genuine, this will be the final edit.