Ahhh, London. When I spent some time there 30+ years ago, I bought coffee from the McDonald's across from the Warren Street tube station (still appears to be there according to Google Maps).
But it was of necessity. It was very difficult to get a good cup of coffee from other UK fast food outlets. Has coffee caught on in the UK? At the time, coffee seemed to be mostly an after dinner drink.
Also the new self service kiosks make ordering a bit less grim http://burgerlad.com/2015/02/mcdonalds-touch-screen-ordering...