Thanks for your replies ,I suppose Rita for purely financial reason,s, I don't want to have to register/unregister a UK  car/van in Spain, then drive back to the UK and have hassle expense once back.
So if you leave Spain toward,s the end of your 6 months,  I wonder is there any time limit on your return ? also I am sure there is a problem with UK car insurance and only being OK driving abroad for a certain number of day,s  the 1 time I did drive down, I took out extra cover,that,s when I heard about insuring through Gibraltar, but as I mentioned I never looked into it, and it,s a few years back now.
Thank again for any advise ;D