evidence: If the UK leaves the EU without a deal, British passport holders will be considered third country nationals by countries within the Schengen area after 29 March 2019. [...] Since 2001, some adult British passports were issued with a validity longer than 10 years. If you renewed your passport before it expired, you were allowed to have the time left on your old passport added to your new passport. The maximum validity period possible was 10 years and 9 months. This means you can’t use the expiry date to check if your adult passport will be valid under the new rules. Since the beginning of September 2018, extra validity was no longer added to passports. The maximum validity for an adult UK passport is now 10 years, and 5 years for a child passport. We have made this change to follow recommendations set out by the International Civil Aviation Organisation and to provide clarity about passport validity in the future.