[Milu]

Transferring title in the uk is very easy.
At the bottom of the registration document (log book) there is a tear off slip. I don't have mine at hand but I think the current owner completes one part and you the other. Just follow the simple instructions, complete and post to DVLC Swansea. The new registration document is then posted to you.

I would suggest that the first step would be to contact your own transport bureaucrats and establish what paperwork THEY need. I suspect you would also need a valid bill of sale, MOT certificates and possibly tax discs. You may also need to pay tax on the used value of the car before it can be formally imported and registered - this may be a good negotiating point when buying.

If Spanish bureaucracy is like Italian I would concur with using an experienced specialist (the gestoria?) as Dean said.