...and coming in a close second :-
Gresham Hotel Bloomsbury
"Hotel from Hell"... "Purgatory"... "Oh My God!"... "I also fell victim to this depressing, dirty and unfriendly hellhole".
And the moral of the story - never believe a word on their website, go to sites like TripAdvisor that actually have real people telling you what the place is like.
Poor people who had to stay in these places.