I have to agree with One Aldwych- the only caveat is DO NOT book the smallest room category. Also worth joining the (free version) Leaders Club- they honour benefits very well here. This is a lovely hotel.
The other London hotel I have used which IS NOT luxury, but does have beautiful top floor suites in a convenient area (for some) is the Zetter- the suites with private terrace on the top are very good value and have great B&O entertainment systems as well (the hotel is at most 4* however)... if you want to be in that area however this is the only option.