Dear Madam,
According to the Spanish Law, if you are an spanish citizen you should change your surname in the Civil Registry. Also, you should explain in the Registry the main reason ( according to the british custom, you prefer the surname of your husband).
If you are not spanish, the change would be done in the British Registry. You will receive a new passport and you will be able to sign the documents with your spanish surname.
I do not recomend you to use the new surname before the legal change in order to avoid problems with your actual identity card (passport or residence card)
If you have any question, do not hesitate to contact us.
Javier Mar?n
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