Acquiring Spanish citizenship isn’t always a straightforward decision for UK nationals living in Spain.
Spanish law stipulates that to become a Spanish citizen, it's necessary to submit a written renunciation of one's original citizenship.
More specifically, Article 23 of the Spanish Civil Code establishes that to acquire Spanish nationality "by option, naturalisation, or residence," it is necessary "for the person to declare that they renounce their previous nationality."
There are exceptions relating to dual nationality agreements with certain countries (Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Puerto Rico, Uruguay, Venezuela, Portugal, Andorra, France, Philippines, Equatorial Guinea and Sephardic Jews of Spanish origin).
There are also some caveats for UK nationals who have a birth right to Spanish citizenship (because they have a Spanish parent, for example).
But for Britons applying for Spanish citizenship via residency - in the majority of cases after legally and continuously residing in Spain for ten years - renunciation of British citizenship is technically mandatory in Spain.
However, Spanish authorities do not verify whether the renunciation was registered in the country of origin, in this case the United Kingdom.
So what does this unofficial renunciation of British nationality mean? Would a Brit who became a naturalised Spanish citizen lose his or her British citizenship if UK authorities were to find out about them becoming Spanish?
No. The 1981 British Nationality Act stipulates that British citizenship can only be lost by renouncing it before British authorities.
According to gov.uk, “A person can apply to give up (renounce) their British citizenship. Losing or renouncing British citizenship affects a person’s right to live in the UK. It can also affect the status of any children born to them on or after the date of renunciation.
This must be done by submitting a renunciation to the Home Secretary (here’s a guide on how to do it), who will not accept it unless the person already holds or intends to acquire another nationality.
It’s worth noting that the British Nationality Act even allows people who have renounced their British passport to obtain the nationality of another country to reapply for UK citizenship.
Even though Brits in this situation may be relieved to find out that there is no threat of them losing British nationality, what do Spanish authorities make of this? Could Brits lose their newly acquired Spanish citizenship?
The answer is yes and no.
In a 2007 resolution by Spain’s Directorate General of Registries and Notaries, published in the country’s BOE official state bulletin, "the renunciation of the previous nationality" is described "as a mere formality," regardless of whether or not that renunciation is legally valid in the foreign country.
In 2025, the Spanish government confirmed that the Civil Code requires individuals to declare their renunciation of their original nationality, but there is no "legal basis for demanding proof of the loss of their previous nationality."
In a nutshell, you have to sign a waiver saying you’re renouncing your nationality but Spain is not going to demand proof you’ve actually done it.
Nevertheless - and this is important - Brits who have become naturalised Spanish citizens can lose their newly acquired Spanish citizenship.
The Spanish Civil Code stipulates that those who use a nationality they renounced for three years after acquiring their Spanish one will lose their Spanish nationality.
The Spanish Justice Ministry also states that “Spaniards who are not Spanish by origin (for example, those who have acquired Spanish nationality by residence) will lose their Spanish nationality if (...) after acquiring Spanish nationality, they use for a period of three years the nationality they had renounced when acquiring Spanish.”
Similar rules apply for those who’ve acquired Spanish citizenship and reside abroad, and/or have acquired a new nationality.
So for the three years following the acquisition of Spanish citizenship, make sure to use your Spanish passport most if not all of the time.
The general advice for naturalised Brits arriving in or leaving Spain is to use their Spanish passport and/or DNI (Spanish ID card) at the airport in Spain.
If they're going to the UK they should use their British passport when entering and leaving, especially with the new rules for British dual nationals.
READ MORE: Will British dual nationals really be forced to have a valid UK passport from February?
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