Second hand car faulty?

[foogie100]

My girlfriend bought a car on Monday 17th May via a private transaction. The car seemed to be in reasonable working condition, had a full MOT and was in good exterior condition. The day after we bought it (today) the electrics began to fault, the dash display, the side lights and the radio did not turn off when the car was turned off and this ran the battery dry. Upon inspection it became apparent that the dealer (or someone else) had short circuited the wiring to the fuse box so that the car would run temporarily. We think that the people who sold us the car did this deliberately. What are the legal rights in this situation regarding second hand dealers and has anybody had any prior experience of this sort of thing in the past? (UK law only please!)