A car you already own usually comes with you when you move. The paperwork does not travel so easily. Spain taxes registration by emissions, checks the car at the ITV, and issues plates only when the file is clean. Here is the order that works, and the two rules people miss.
If you are a resident, your car has to be on Spanish plates. There is a well-known six-month window, and once you are registered as a resident in Spain the clock is running. Staying on a foreign plate as a resident is the shortcut that gets stopped first at a control.
A genuine non-resident, here less than six months a year, can keep the foreign plate on the car and drive it on the original registration. That is why the first question is not how to import, but whether you are legally a resident yet.
The impuesto de matriculación, formally IEDMT, is a one-off registration tax. On the mainland and the Balearics it is banded by the car's official CO2 emissions: 0% below 120 g/km, 4.75% from 120 to 160, 9.75% from 160 to 200, and 14.75% above 200. It is charged on the taxable value of the vehicle, not a flat fee, so a low-emission car can arrive almost tax-free and a big petrol SUV cannot.
The tax is normally paid with Modelo 576 at the Agencia Tributaria. If the car is exempt (for example an official permanent transfer of residence with the conditions met), you file Modelo 06 instead. Do not assume you are exempt; the exemption has its own rules and a deadline.
A car coming from the UK is a third-country import. VAT at 21% can apply on the value, plus any customs duty, depending on its origin and age. A used car that was registered and taxed in the UK before Brexit may qualify for relief, but the file has to prove it. Budget for the import before you ship, not after the car is sitting at the port.
An imported vehicle must pass an ITV, a technical inspection, before it can be registered. This is a homologation check as much as a roadworthiness one: lights, glass, speedometer in km/h, and any modifications have to match the Spanish approval for that model. A ficha técnica reducida is issued so the car has a Spanish technical record.
Once the tax is paid and the ITV passed, you register the car at the DGT. The traffic-office registration fee runs at about €99.77 for most vehicles. You leave with plates, and the car enters the local system for the IVTM, the annual municipal road tax, which is then charged by the town hall where the car is registered.
If you would rather not do it yourself, a gestor handles the whole file for a few hundred euros and saves the queues. For a family arriving in the Maresme with one car and a school run to organise, that is usually money well spent.