The Police car pound in Torrevieja is full of British registered cars stacked on top of each other. An article I have just read gives a clue as to why.

A lady after dropping her children off at school was stopped by police, who asked for documents relating to her British registered Audi. It transpired that she had brought it in the UK and had been driving it in Spain for 10 months.
Although the insurance was still in date, the British tax disk and MOT wasn't, which meant the insurance wasn't valid either. The car was impounded, and she was told that it would need to be on Spanish plates before being released, but wouldn't release it to get this done..As the car was worth a lot of money, a solicitor became involved, and eventually the car was allowed to be taken to the ITV station to be tested before being put on Spanish plates. The cost of the fines, removal and storage, solicitor, and transfer onto Spanish plates cost a great deal of money, as it all took five months..No wonder many decide to pay their fine and let the Police dispose of the vehicle..

Dont risk it.
CD