I have stayed in Tony's lovely flat in Belsize Park on three separate occasions and would definitely stay there again. The location could not be better for public transport, walking, shopping and dining. The flat itself is very clean and well maintained with all the amenities one could want whilst traveling. The bed is extremely comfortable and there is also a comfortable sofa bed in the living room. The only negative is that there are no curtains in the living room so if there are guests sleeping in there it is pretty light in the mornings although the windows are smoked glass so that mitigates the light problem somewhat.
Tony is a great host and will always get back to you promptly if there is a problem.