This explains where the 10 years comes in: https://www.gov.uk/guidance/passport-rules-for-travel-to-europeOn renewing a UK passport any time remaining *was* added to it (doesn't happen now), so you could have been issued with a 10 yr & 4 month passport. The EU will now only recognise the first 10 years, so if you are traveling in the final 4 months of your 10 year & 4 month passport it's not valid for EU travel
Ann Haddleton ● 1909d