you can expect no problems whatsoever

if the car was properly registered in uk and not just some racecar, when he buys it he should make sure to get the ownership document known as the V5 (actually, that does not prove who owns the car, just who keeps it, so he must also get a written receipt showing the name and address of the seller, the registration number and the chassis number and the price).

this is the official government website telling you what to do when exporting a vehicle:
http://www.dvla.gov.uk/vehicles/expt...nent%20Exports

hth and good luck