I suggest a week in London, no more, then hire a car and head out to the west country. Chain hotels are the same as everywhere. Pubs/small hotels are great. Use booking.com and tripadvisor to find the best places/deals and then check them out. I would book ahead in London, but not so necessary elsewhere except for very popular places in July/August. Once into September and the schools go back, it's much easier. Come back here for suggestions when you have a basic itinerary and I'm sure you will get lots of good suggestions.