My wife and I stayed five days at a Best Western on Belgravia Steet seven years ago. It was actually a refurbished flat or house and looked like one from the outside. Pretty decent but no air-conditioning. Since the temps at the time were in the 80s, it was pretty hot at night. Still a fairly nice experience.
I never travel to Great Britain in summer so I’m lucky that I don’t need air conditioning. Two years ago, we rented a flat for two weeks in Chelsea. Everything was great except for the tiny clothes dryer. But then most people in England like to hang their clothes to dry.