http://web.ukonline.co.uk/martin.nail/regional.htm
I think you will find this very useful. It gives the names of clubs all over the regions of England, contact numbers and the rest.
Obviously there are things you must see like Shakespeares house in Stratford and Robin Hoods tree and London of course.

With this site you can choose clubs round where you are going anyway. Also you should take in one festival.. sidmouth is in Devon which is one of the beautiful parts of England, the south west.

Froots is an English folk magazine and they have a list of all the festivals - probably on their website.

have a good time!