I would not buy a Spanish car in the UK.
Getting a car purchase wrong for Spain could have serious consequences.
For example: It's vital to ensure that no debts are attached to the car. These can be outstanding finance and perhaps more seriously , traffic fines. If there are uncleared fines relating to the car, you may wind up being pursued for them.
If there is outstanding finance, you would simply lose the car when the recovery agents show up.