If you use a good Notary in the UK, such as the one I use in Picadilly. London, they are prepared to draw up a simultaneousley translated text. i.e. half the page in English with the Spanish translation at the side. Thus you don’t need to get an official translation since the document is produced by an office with a recognised Spanish Notary in house. It also saves carrying around 2 documents and you can easily check the meaning.