Hi guys - thanks for the responses and suggestions. The story so far; I have the Atos taxed, insured and ITV (same as MoT) in Spain and have driven it to the UK. I've had the lights changed and the car has now passed it's UK MOT. I can't keep it on Spanish registration unless I take it back to Spain every 2 years for a new ITV - which I would need to renew the Spanish (drive anywhere in Europe) insurance. Also, now it has UK lights it wouldn't pass an ITV! So I need to "import" it into the UK. The car was manufactured in India and I've written to Hyuandi Motors India Ltd to ask for the copies / originals that the DVLA want -"the original non-UK registration certificate or export certificate" but have not had a response yet to 2 emails.
I didn't get a V5 (Certificado de Registro de Automovil) when I bought the car, although I do have proof of ownership and am registered to pay road tax at my Spanish town hall.
Further to Ruperts Trooper's suggestion I'm going to see how I can get a copy of the Spanish "V5" today. Thanks for your time and trouble. Alan