I'm not really sure (and asked my mum, who's visiting right now, and she's not either) having not actually stayed in very many hotels in Britain...and never as an "univited guest". But we both think that possibly the worst that would happen would be that they ask you to leave and/or pay for the night. I think how stringent hotels are probably varies quite a bit from one to another.

Sorry I can't be more help.

On a different note though, I have an extra reservation for the dinner Saturday night as my son...who's staying with me will be off visiting some friends... If you're interested, let me know and I'll let you have it for a lot cheaper.