Those of you planning to drive through France in order to return to the UK, should be aware that the French authorities have updated their attestation (declaration), which anyone entering and/or travelling in France is required to carry to explain their reason for their journey. It must be presented to transportation companies (eg ferry, EuroTunnel) and border authorities. You may also be required to show it if you are transiting through an airport in France on your way to the UK. You have to indicate your specific reason for travelling on the form. In most cases this will be “individuals transiting through France to reach their residence, accompanied by their spouse and children”. It is essential that you carry this document, along with your passport, residency certificate (if returning to Spain) and any evidence of your onward journey (e.g. ferry/rail ticket). The Embassy in Paris has produced this helpful note explaining more: https://www.facebook.com/notes/british-embassy-paris/new-international-attestation-which-attestation-to-use-and-when/3597961756942986/
To download the attestation and for more information on travelling through France visit https://www.gov.uk/foreign-travel-advice/france