We stayed on a Saturday night in a wonderful heat wave. The cooling interior was very welcoming as you entered. Check in was efficient and friendly (often you can feel "just another guest" - but not so here). We were shown to the lifts - we declined being shown to the room although it was offered. We had been upgraded to a small suite which was wonderful , especially as we were staying on a "reward" night so we were not paying.
The room was quite large for London, very contemporary, beautiful linen/cushions, bed very comfortable, electronic drapes, well stocked hospitality tray with fresh milk not the horrible little cartons you often get and an nespresso machine, There were satin padded,hangers to use, a must in my opinion, umbrella, robes, slippers etc. All good.
The bathroom was huge, shower amazing (rain shower or standard) and there were good quality Molton Brown products available.
Staff were very friendly and helpful. There was a harpist accompanying the guests taking afternoon tea - lovely. We didn't eat at the hotel, having other arrangements so am unable to comment on that.
Our room was quiet, facing the street on the first floor. However it was the weekend and so very little traffic generally in this area. It may be there will be some road noise if you stay mid week. Also, you could hear the slight rumble of the tube trains - you are very close to St James Park underground. It did not disturb my sleep but I was aware of it once I was awake although when the radio is on you don't really notice it. It may not be heard on higher levels.
Would I stay again - YES. It is also very convenient for most of London and easy walking distance to Parliament, Piccadilly, Mayfair and West End.