The Bar/Lounge at The Westminster London, Curio Collection by Hilton
Doubletree by Hilton London - Westminster's bar/lounge is endorsed by reviewers writing for major publications. Out of 7 professionals tracked on TripExpert, 4 recommended the bar/lounge, including Fodor's, Zagat and Oyster.
The Westminster London, Curio Collection by Hilton 
Fodor's
Zagat
Oyster
Star Service
Fodor's "The restaurant and bar serve modern British cuisine"
Zagat "Extras include a restaurant, lounge and fitness room"
Oyster "Hotel features like a paid lounge that serves food throughout the day, five meeting rooms, a
fitness center, and free Wi-Fi round out the facilities -- though breakfast costs extra"
Star Service "Guests in suites and executive rooms have access to the Executive Lounge for breakfast, tea and coffee, soft drinks, alcoholic drinks and nibbles"
