Dual British–Spanish nationals and the UK ETA: which passport, which rules?

From 2026, the UK’s Electronic Travel Authorisation (ETA) scheme is reshaping how many people travel to the UK. For dual British–Spanish nationals, the rules can look especially confusing.

This guide explains, in practical terms, what happens if you are a Brit who has become Spanish, what the law says about dual nationality, and — crucially — which passport to use at each stage of a Spain–UK journey.

Worried the oath you took makes you a fraudster? Read this first.

Many Brits who have naturalised as Spanish come to us with a version of the same fear: “I took the oath, I declared I was renouncing my British nationality, and I’ve still got my British passport in a drawer. Am I in trouble?”

The short answer is no — and here is why.

The renunciation declaration you made is a Spanish law formality. It has no effect whatsoever in UK law. The only way to lose British citizenship is to sign a formal renunciation to the Home Office and pay the fee. Spain knows this perfectly well. The declaration is not a trap.What Spain actually cares about is straightforward: be Spanish in Spain. Use your Spanish documents with Spanish authorities, cross the Spanish border on your Spanish passport, and Spain will have no interest in what passport you use in Leeds or London. Spain is pragmatic about this. Nobody is going to knock on your door because you visited your family in the UK on a British passport. The civil registry rarely goes looking for undeclared dual nationals. Difficulties only arise if something else — a contentious legal matter, for instance — draws attention to your file, and someone starts asking whether you have been acting exclusively as British while ignoring your Spanish nationality entirely.

The rest of this guide explains how to travel correctly and stay comfortably on the right side of both systems.

Key points at a glance

Question	Answer
Do I need a UK ETA if I am both British and Spanish?	No. As a British citizen you are ETA-exempt. The problem only arises if you travel on your Spanish passport alone.
Which passport at airline check-in in Spain for a UK flight?	Show your British passport so the airline sees you as a British citizen who does not need an ETA. Have your Spanish passport with you as well.
Which passport at the border?	Spain (exit and entry): use your Spanish passport. UK (arrival and departure): use your British passport.
Is it a problem to use both passports?	The real risk is not owning two passports. It is using the wrong one in the wrong place — or never using your Spanish nationality at all over long periods.
What is the safest pattern in practice?	Be Spanish in Spain (Spanish documents and borders) and British in the UK (British passport and UK dealings). Carry both passports when you travel between the two.

1. British, Spanish… or both? The legal background

The UK and Spain take different formal approaches to dual nationality — but in practice the gap is smaller than it looks.

The UK allows dual and multiple citizenship. You do not lose British citizenship just because you acquire another nationality. To give up British citizenship, you must sign a formal renunciation to the Home Office.

Spain formally requires naturalising citizens to declare they are renouncing their previous nationality. In practice, however, Spain’s approach is pragmatic: it treats you as Spanish on Spanish territory and is not in the business of policing what passport you use elsewhere.

After naturalisation, Spain expects to treat you as Spanish while you are in Spain. Spanish nationality can, in theory, be lost if you stop using it entirely and rely exclusively on another nationality for a number of years while living abroad — but this is not something Spain actively investigates.

The practical upshot:

In UK law, you remain British unless you actively renounce to the Home Office. The Spanish declaration changes nothing in UK law.
In Spanish law, the expectation is simply that you act as Spanish in Spain — not that you surrender your British passport or pretend it does not exist.

2. What actually happens in real life

On the ground, many long-term British residents in Spain have done the following:

Lived in Spain for years, then naturalised as Spanish after Brexit.
Signed the renunciation declaration Spain requires.
Kept their British passports and continued to use them for UK-related matters.

In practice, they typically:

Use a Spanish passport or DNI in Spain — for healthcare, voting, and crossing the Spanish border.
Use a British passport for the UK — to enter and leave the UK, and for dealings with UK authorities.

Spain does not ask you to hand in your British passport when you become Spanish, and there is no automatic switch that tells the UK to cancel your British status. You end up in a familiar and entirely manageable position: Spanish in Spain, British in the UK.

3. The ETA twist: why dual nationals are nervous

The UK ETA scheme adds a practical wrinkle:

Non-visa nationals (including Spaniards) generally need an ETA to travel to or through the UK, unless they are exempt.
British citizens are ETA-exempt. The UK expects British nationals to travel on a British passport.

For a dual British–Spanish national, this matters:

If you book and travel only on a Spanish passport, the airline’s system will treat you as a Spanish citizen who needs an ETA.
You cannot apply for an ETA as a British citizen — British citizens are not meant to use ETAs at all. They are supposed to use their British passports.

That is why many dual nationals have found that travelling on the wrong passport can cause real problems at booking and check-in. The fix is simple: use the right passport in the right place.

4. Which passport to use — a step-by-step guide

Here is the practical pattern, shown as a table.

Stage	Spain → UK	UK → Spain
Airline check-in	British passport (proves ETA exemption)	British passport (or both)
Departure border control	Spanish passport (exit as Spanish citizen)	British passport (exit as British citizen)
Arrival border control	British passport (enter UK as British)	Spanish passport (enter Spain as Spanish)

The key message:

You may show both passports on one journey.
Use your British passport wherever the UK’s entry rules are being checked (airline check-in for a UK-bound flight and the UK border).
Use your Spanish passport for Spanish border formalities and dealings inside Spain.

5. Staying comfortably on the right side of both systems

Spain’s approach is pragmatic, not punitive. The authorities are not monitoring dual nationals or looking for people to catch out. What matters is the pattern of behaviour, not the existence of a second passport.

The comfortable pattern — which most dual nationals already follow instinctively — is:

Be openly Spanish in Spain: use your Spanish passport at the Spanish border, your DNI with Spanish authorities, and register with the consulate if you are living mainly in the UK.
Be openly British in the UK: use your British passport at the UK border and for UK dealings.
Avoid very long stretches where you never act as Spanish at all — no Spanish passport renewal, no consular registration, no engagement with Spain whatsoever. That is the pattern that could, if something else went wrong, attract questions.

For most people, the reassurance is simple: if you are already living as Spanish in Spain and British in the UK, you are already doing it right.

6. When to get tailored advice

This guide is deliberately general. You should get individual advice if, for example:

You have a complicated nationality history — Spanish by descent, British by birth, other nationalities in the mix.
You have criminal or immigration issues in either country.
You are worried about possible loss of Spanish nationality because of how you have used your passports in the past.

For most Spain-based Brits, however, the core message is simple:

You do not need an ETA as a British citizen.
You do need to carry and use the right passport in the right place.
It is possible — and often sensible — to travel with both passports and present each one where it belongs.

Need advice on dual nationality or travel documents? Dual-nationality travel questions are rarely just about passports. They can touch on your immigration status, your rights under Spanish law, and what happens if you ever need to rely on UK protection abroad. If you have any doubt about which passport to use — or whether your dual nationality is secure — it is worth getting specialist advice before you travel.Migrant Law Partnership offers expert immigration advice on complex nationality and travel document issues. Contact us to arrange a consultation.Call: 020 7112 8163 Email: hello@migrantlawpartnership.com WhatsApp: +447849608399