Yes, you absolutely need a valid passport to travel by ferry from the UK to Spain in 2026. Since the UK is not part of the EU or the Schengen Area, all passengers must clear border controls at both the departure and arrival ports (such as Portsmouth/Plymouth in the UK and Santander/Bilbao in Spain). Under the current Schengen Area rules, your passport must have been issued within the last 10 years and must be valid for at least three months beyond your intended date of departure from Spain. Furthermore, by late 2026, UK citizens will also be required to have an approved ETIAS (European Travel Information and Authorisation System) waiver linked to their passport before boarding. Ferry operators like Brittany Ferries are required to check these documents during the check-in process at the terminal; if you do not have a valid passport, you will be denied boarding. This requirement applies to all passengers, including infants and children, who must each have their own individual travel documents.