I don't know that you can do it legally! I am not an expert! i would email the details of the car to a gestor, here is the email of one we use in Mazarron, administracion@gestoriamazarron.es
I assume the car has French head lights still, suitable for driving on the continent, so that's one less expense. The gestor above have an English speaker so you can email in English.
Insurance?? Email Julie at IBEX in Camposol for advice, Julie.mcgovan@ibexinsure.com
I don't know how/ if you can get insurance for French reg car in UK...I assume must be okay. But when reregistered onto Spanish plates I think that policy will have to be cancelled and a new policy issued.
what about getting it transported over, approx €595, transport direct to garage or your apartment here. I would recommend transporting direct to Decklid in the Port, email decklid@hotmail.co.uk then he can sort ITV and transfer for you, hope this helps,