We spent 2 wks in the UK in May 2004. It rained the first day we arrived and the last day before we left. In between, the weather was good. Maybe we were lucky...

Here are a few B&B's for around 25-30 GBP per person that I found in the Cotswolds:

http://www.alderleyguesthouse.com/

http://www.corshamfield.co.uk/bookings.htm

http://www.mousetrap-inn.co.uk/

http://www.theblenheim.com/Page_1x.html

http://www.snoozeandsizzle.com/

http://www.cotswoldstay.co.uk/tariff.htm

As you can see, there are quite a few that I've found so far and I'm sure there are many more.

Just a suggestion if you are on a budget. I would pick 1 place (possibly the Cotswolds) and rent a cottage for a week. Then choose somewhere else for the other few days. I find that it is much cheaper staying in a cottage than hotels / b&bs and you can also save on food. I have used welcome cottages for the Cotswolds, Cornwall and Scotland and have been very pleased.
Another cheap option is staying in travelodges for the odd night.
Good luck,
Carolena

Yes a BritRail pass will save you money for doing what you seem to be doing - can't buy them in UK nor any equivalent all-line pass as cheap as from outside UK - UK residents can't use BritRail so not sold there. I always recommend BETS (www.budgeteuropetravel.com) for their expertise in UK trains and not charging some of RailEurope's fees - request on their home page their free European Planning & Rail guide - it has a chapter on Britain - not only trains and passes but itineraries and bits on most of the places you're going. www.ricksteves also has good info and i've heard good things about www.euraide.com. If you weren't going to Scotland the BritRail England pass would be cheaper.

I'd like to add my 4penn'orth (a bit of lancashire dialect!). I live in Stratford on Avon and it CANNOT be described as a city. It's a small market town with the Royal Shakespeare Theatre, Shakespeare's birthplace and a riverside setting. It's within easy reach of the Cotswolds- Chipping Campden must be one of the prettiest villages in the country and sheep, rolling pastures and hills with plenty of walking footpaths through gorgeous countryside. Coach trips from Stratford to the Cotswolds every day. I can recommend an inexpensive but really welcoming Bed and breakfast Appletrees, 194 Evesham Rd tel 01789 298508. Some friends stayed there recently and were very impressed.
Also within easy reach of Stratford- Warwick Castle (will occupy you for a whole day); Kenilworth Castle and Coventry Cathedral. You can take a train or bus (45mins) to Oxford. Non-one takes a car into Oxford anyway- it's impossible to park!
London Marylebone for the trains to Stratford on Avon -journey time about 2 hrs. or coach from Victoria Coach Station.
Consider Stratford for part of your trip and maybe another base somewhere like York