Getting UK Car registered into Spain

https://www.spanish-number-plates.com/ 

Highly recommended on the forum, Leigh is the expert and you know you will not get ripped off unlike another operator I could mention.

Most important is a so called COC (Certificate of Conformity) issued by the manufacturer. w/o this document better forget the whole thing. Your vehicle must be imported and taxes and fees apply. Contact any customs broker for an estimate before you decide. Drive your car to the next ITV and get a "Certificado de Caracteristicas Tecnicas" for some 80,- Let a Gestoria do the rest, should not be more than 100,-

I did it myself a few years back, however the previous poster is correct, you will need a COC (Certificate of Conformity).  I obtained mine direct from the vehicle manufacturer’s homologation dept.

Check the rules / regs, if you are applying for residencia, then you use to be able to import the vehicle tax free.

The other document, Certificado de Caracteristicas Tecnicas was very simple to obtain, basically the office is located at the back of the ITV station in Torrevieja. The tiv control register

One thing others have not mentioned is that you may have to change your headlights.  Using the 'sticky patch' to alter the beam will not be accepted to register your car.  Also, if you have different make of tyres on the same axle.  These will need to be changed also.

Leigh will take care of the COC, or lack of. IIRC it's an extra 100 euro for an engineers report.

He can also supply and fit new headlights and arrange wiring for the fog light (if required).

Highly recommended, he did ours last year