I did tailwheel difference training at Northants School of Flying and was very pleased with the instructor, the aircraft, and the airfield (it is particularly suitability for taildragger training).
I would suggest that if Tatenhill is a possiblity for you, you consider the type of flying you will be doing, after your training. Tatenhill has four runways and the choice of grass and concrete. The Decathlon at Tatenhill is also very powerful. If you expect to fly a Pitts and occasionally (or regularly) have to fly off tarmac, then Tatenhill will get you upto speed more cost-effectively than most places.
If you have your own aircraft or access to a taildragger for training, I can also recommend a Midlands-based freelance instructor who is excellent. PM me if this is an option for you.