There's
Hotel Endsleigh in Devon. You'd have to do a bit of research though because I've read some bad trip reports concerning management as well as the dining, but it looks like a an absolutely stunning place to stay in the English countryside. I've always wanted to visit.
If you're staying within the city (London), there's always The Dukes and Blakes Luxury Hotel. Two more I've always wanted to try out while overseas.