Spanish nationals living in the UK may need to take extra steps after acquiring British citizenship. This is especially important after Brexit, as many Spanish nationals in the UK have applied for British naturalisation while still wishing to keep their Spanish nationality.

The key issue is timing. The Spanish Consulate in London explains that, to avoid losing Spanish nationality, a person must request conservation of Spanish nationality before three years have passed from acquiring the foreign nationality, or from emancipation if the foreign nationality was acquired as a minor.

For Spanish nationals who become British, this may mean making a formal declaration to preserve Spanish nationality and preparing supporting documents, including an apostilled UK certificate of naturalisation.

This guide explains the document legalisation side of the process, why an apostille may be needed and what to check before your deadline.

Why Spanish nationals may need to act after becoming British

Spain does not treat every dual nationality situation in the same way. For Spanish nationals who voluntarily acquire another nationality while living abroad, Spanish nationality may be at risk unless they complete the required conservation declaration within the correct time limit.

The UK is not one of the countries usually covered by Spain’s special dual nationality arrangements. This means a Spanish national who becomes British should not assume that Spanish nationality will be retained automatically.

The safest step is to contact the Spanish Consulate or Civil Registry as soon as possible after acquiring British citizenship and check the exact conservation requirements for your case.

The three-year deadline

The three-year deadline is one of the most important points.

According to the Spanish Consulate in London, the conservation of Spanish nationality must be requested before three years have passed from the acquisition of the foreign nationality.

For many people, this means the clock starts from the date they acquired British citizenship, which is usually linked to the date of naturalisation.

Do not wait until your Spanish passport renewal is due. If you miss the deadline, the process may become more complicated and you may need advice on recovery of Spanish nationality rather than simple conservation.

What is the conservation of Spanish nationality?

Conservation of Spanish nationality is a formal declaration that you wish to keep your Spanish nationality after acquiring or holding another nationality.

The Spanish Consulate in London describes it as the act by which a person expresses the wish to preserve Spanish nationality when they acquire or hold another foreign nationality.

This is not the same as applying for Spanish nationality. It is a declaration made by someone who is already Spanish and needs to preserve that status after acquiring another nationality.

Why a UK certificate of naturalisation may be needed

If you have become British through naturalisation, your UK certificate of naturalisation is usually the key document proving when British citizenship was acquired.

The Spanish authority may need to see this certificate to confirm:

• that you acquired British citizenship
• the date of naturalisation
• your full name
• your date and place of birth
• your certificate details
• the deadline for conservation of Spanish nationality

Because the certificate is a UK document being used before a Spanish authority, it may need to be legalised with an apostille.

Why the certificate of naturalisation may need apostille

An apostille confirms that the relevant UK signature, seal or certification on a document is genuine for use abroad.

In the UK, apostilles are issued by the FCDO Legalisation Office. The UK Legalisation Office checks the signature, stamp or seal on a document and legalises it by attaching an apostille.

For Spanish nationality conservation, the Spanish authority may ask for your UK certificate of naturalisation to be apostilled before it is accepted.

Because the certificate of naturalisation is an important citizenship document, many applicants prefer to apostille a solicitor-certified copy rather than risk sending the original, where the consulate accepts this route.

Original certificate or certified copy

Before arranging the apostille, check whether the Spanish Consulate requires the original certificate of naturalisation or accepts a solicitor-certified copy.

A certified copy may be useful because:

• the original certificate is valuable
• replacement can take time
• the document may need to be posted
• the consulate may only need legalised evidence of the certificate
• you may need the original for other purposes

However, you should not assume a copy will be accepted. Always check the current consular instructions before preparing the document.

Documents that may be required

The exact document list depends on the consulate, your personal circumstances and the current procedure.

Documents may include:

• Spanish passport
• Spanish DNI, if held
• UK certificate of naturalisation
• apostilled certificate of naturalisation or apostilled certified copy
• birth certificate
• proof of address in the UK
• consular registration details, if applicable
• completed consular form
• evidence of name change, if applicable
• passport or identity document copies
• appointment confirmation or email instructions from the consulate

The Spanish Consulate in London publishes consular information for Spanish nationals in the UK and provides contact details for nationality and civil registry enquiries.

Translation requirements

The Spanish authority may require documents in Spanish or may request a translation of the UK certificate of naturalisation.

The correct order matters. In some cases, the UK document should be apostilled first and then translated. In other cases, the consulate may provide specific instructions about translation format, sworn translation or whether translation is needed at all.

Before arranging translation, check whether the consulate requires:

• the apostilled UK certificate
• a certified copy
• a sworn Spanish translation
• translation of the apostille
• translation completed by a sworn translator
• original documents and copies

Translation rules can vary, so do not order a translation before confirming the latest instructions.

How to prepare your certificate of naturalisation for Spain

The process usually works as follows.

1. check your deadline

Confirm the date you acquired British citizenship and calculate the three-year deadline. Do this early, especially if your deadline is close.

2. contact the Spanish Consulate

Ask the consulate or Civil Registry which documents are required for conservation of Spanish nationality and whether they accept an apostilled certified copy of your certificate of naturalisation.

3. prepare the certificate

If a certified copy is accepted, arrange for a UK solicitor or notary to certify a clear copy of the certificate of naturalisation.

4. arrange FCDO apostille

Submit the original certificate or certified copy for FCDO apostille, depending on the consulate’s instructions.

5. arrange translation if required

If a Spanish translation is required, confirm whether it must be completed after apostille and whether it must be a sworn translation.

6. submit the declaration

Follow the consulate’s process for making the declaration of conservation of Spanish nationality.

Common mistakes to avoid

Common mistakes include:

• waiting until the Spanish passport renewal date
• missing the three-year deadline
• assuming Spanish nationality is retained automatically
• sending an uncertified photocopy of the UK naturalisation certificate
• apostilling the wrong version of the document
• translating the document before checking the correct order
• using outdated consular instructions
• failing to check whether a certified copy is accepted
• leaving no time for apostille, translation or appointment delays
• assuming advice for another country applies to Spain

These mistakes can create delays and may make the nationality process more complicated.

After the three-year deadline

If the three-year deadline has already passed, the process may be different.

You may need advice on loss or recovery of Spanish nationality rather than simple conservation. The correct route depends on your personal circumstances, including whether you are Spanish by origin, where you live and how Spanish nationality was acquired.

This is a point where specialist Spanish nationality advice may be needed. An apostille service can help prepare and legalise UK documents, but it cannot decide your nationality status.

How we can help

We can help with the UK document legalisation side of retaining Spanish nationality after becoming British.

Our service can include checking your UK certificate of naturalisation, preparing a solicitor-certified copy where accepted, submitting the document for FCDO apostille and advising on the correct order for apostille and translation.

If you are preparing a conservation of Spanish nationality declaration, send us the consulate’s document instructions and your UK certificate type. We can help confirm which UK documents need apostille before you submit them.