Foreign plates (anything but Spanish) are permitted ONLY 30 days in Spain if you're a resident. Rule changed from April 2017. If caught you will be fined up to 500 euros, your car impounded for almost six months at 9 euros per day until the vehicle is on Spanish plates!
The police are currently upholding the laws of If you are a Spanish resident you have 1 month to change the plates to Spanish and if non resident 6 months in total of keeping your vehicle in Spain total in any 12 month period after this it must be removed (Information updated 31st May 2017)
Registering a non-Spanish vehicle in Spain can be a complex and costly procedure. However you my be exempt from Spanish registration tax by getting Spanish number plates within on month of entering the country, but to do this you need to become a resident.
STEP 1 - OBTAINING A CERTIFICATE OF CONFORMITY
This is a statement by the car´s manufacturer that it conforms to EU regulations. You will need the car´s chassis number to complete this straightforward process on line at www.eurococ.eu/eu/certificate_of_conformity. The charges for this service will vary according to the type of vehicle make and the country of first registration.
STEP 2 - CURRENT LOG BOOK
The vehicle's original log book showing your name, the vehicles age, and a valid UK address. You will also need a receipt for the purchase of the car.
STEP 3 - RESIDENCY IN SPAIN
The Spanish Residency Certificate is your official proof of residency in Spain. Details on residencia HERE
STEP 4 - OBTAINING A SPANISH MOT CERTIFICATE
All vehicles over 4 years old must be roadworthy and clearly display a valid ITV, Details on how to get a ITV can be found HERE
STEP 5 - OBTAINING A SPANISH EQUIVALENT OF A TAX DISC
The Spanish Tax Agency can provide your vehicle with a valid tax disc for Spain which must be carried in the car at all times. You will need to complete the relevant form on line and pay the amount according to your car´s tax band.
You can carry out all these procedures yourself or seek the assistance of a gestoria to do this for you .