Edit to add: the booking link is slooooow, try going to the offer landing page instead:http://www.royalgardenhotel.co.uk/default.asp?page=3543§ion=215
Then follow the link in the body of the text.
I just received an email from the Royal Garden Hotel, London. They're running a special £50 room rate to help the Leukaemia Research charity.
You can stay in a superior room for one night at a price of £50 + VAT (total £58.75), as long as you donate £10 to the charity.
So that's a five star hotel room in central London for £68.75. Sounds pretty good to me.
You can only stay a single night at that rate, and only between 28 Jan - 27 Feb. They seem to have blacked out Saturday nights and the whole Valentine's weekend too.
I checked for a room on 26 Feb and the promotion price is available. The best rate for a superior room on that date via the standard booking page is £185.00, so that's a good saving.
Hope it helps someone out.