When I lived in Solihull I used a service called Puma Valet (fantastic guy who has more than 35 years exp).
Having moved to London... it is pretty difficult finding a recommended valettor having relied on one for more than 4 years.
I suffer from MS and sometimes I just don't have it in me to do paint correction detailing. I can easily spend 2-3 hours just clay barring a car. I spoke to a few valet services who said that the clay process should take no longer than 15 minutes but I'm serious and I think 15 minutes is nowhere near enough to get the full benefits of the clay and attend to every panel in detail.