Hi
In order to legally transfer a vehicle the following need to be signed and accompanied by a copy of DNI card for a Spanish citizen or Passport and either Residencia or NIE certificate, ( this is only for transfers using a Gestoria, those who visit Trafico and do it in person over the counter need to have original documents( or copies signed by a notario) from both the buyer and seller.
The form for trafico is as follows.
https://sede.dgt.gob.es/Galerias/tramites-y-multas/tu-coche/cambio-titularidad/9.050_Castellano.pdf
You will also need a signed "Compra Venta" agreement which is essentially an invoice between the two parties. ( Sorry I do not have a link as I am on my machine at home not work.
If you are not going to Hacienda and Trafico(tax office & DVLA equivalent) your self with the registered keeper then you will also need an authorization to act for them( again I have them at work).

You will also have to pay a transfer tax of 6% of the cars tax office value(8% for cars over 2000cc).

Rest assured the Spanish system is not user friendly or straightforward. Come down and see me, bring the car details and I will do my best to help.

Thanks for the information James, I will contact the owner and tell him all this, he thinks its quite straightforward. Will come down and see you. Cheers.

we did a transfer recenty, cant remember what we needed but it was dom by a bloke called maguel who goes in Jacks bar a lot, he speaks Spanish and did it the next day for 60 euro. if you want ill get his number as he does it all the time.