Also, depending on what aspects of London gay nightlife you're looking for, the Trafalgar Hilton will put you quite close to Heaven -- home to the G-A-Y dance club on Friday and Saturday nights (and many Thursdays). Most people seem to have a fairly polarized view of the place, but for me it's one of my favorite gay clubs to go out dancing pretty much anywhere.

BTW, it can be a little hard to find -- it's basically under Charing Cross station and reached by a side-street.