Due to changes in validity since leaving Europe, your passport is now only valid for 10 years from the issue date on your passport.
If your passport was issued prior to the UK leaving the EU with additional months on, those extra months are no longer valid.
Passport issue date 21st Jun 2012
Passport expiry date 21st Dec 2022
Your passport expiry date is now the 21st Jun 2022
Most countries in the EU require that your passport is valid for 6 months on the date of return from your holiday, some countries it’s 3 months, meaning the last date you could return on the above example would be the 21st Dec 2021.
You can check if your passport is valid on the below link: