There is a theory test centre in Stratford-upon-Avon:

Packwood House (2nd flr)
Guild Street
Stratford Upon Avon
Warwickshire
CV37 6RP

or search for other theory test centers

There are two sections to the Theory Test:

Hazard perception (where you need to click when you see a Hazard)

Mulitple choice questions of which you need 30 out of 35 marks to pass.

The best books to help you study are the highway code and the D.S.A. complete theory test for cars. These books can be borrowed from Keith. The best simulated hazard perception tests on CD rom can be bought from WH Smiths or Amazon