LOL just found this , hope it is helpful to someone else too
http://www.direct.gov.uk/prod_consum_dg/groups/dg_digitalassets/@dg/@en/@motor/documents/digitalasset/dg_065264.pdf
A quick look at DVLA says :-
What to do if you are selling your vehicle privately to someone
that does not have a GB address
You should fill in sections 6 and 10 with the new keeper’s name and address. Both you and the new keeper (buyer) must sign and date the declaration in section 8. Give the whole V5C to the new keeper to aid registration abroad.
You should then send a signed letter to DVLA, Swansea, SA99 1AG giving the vehicle’s registration number, the make and model of the vehicle, the date of sale or transfer, and the name and address of the new keeper.
Once we know about the change of keeper, you should receive an acknowledgement letter to confirm that you are no longer responsible for the vehicle. If you do not receive the letter within 4 weeks, please phone 0300 790 6802. If you are deaf or hard of hearing and have access
to a textphone, phone 0300 123 1279 (this number will not respond to ordinary phones).