How long must my passport be valid for France?
For someone travelling on a full British citizen passport from the UK, France requires the passport's issue date to be less than 10 years before arrival and its expiry date to be at least three months after the date the traveller plans to leave the Schengen area. Check the two dates separately.
First check the issue date
Count back from the planned arrival date. A passport issued 10 years or more before arrival does not meet the stated rule, even when the printed expiry date is still in the future.
This matters particularly for some passports renewed before 1 October 2018, because extra validity could previously be added. The current French entry rule focuses on the actual issue date for the 10-year check.
Then check the expiry date
Count forward from the date you plan to leave the whole Schengen area, not merely the date you drive out of France. If the trip continues through Belgium, Spain or another Schengen country, use the final Schengen departure date.
The expiry date must be at least three months after that date. Do not combine this with the issue-date calculation: passing one check does not prove the passport passes the other.
Recheck if the route changes
A later arrival or later Schengen departure can change the result. Check each traveller's passport and use the FCDO page again shortly before departure. The guidance is for the common full British citizen passport case; another nationality, passport type, residence status or purpose of travel can have different rules.
Passport validity is also separate from the 90-days-in-180 visa-free allowance. A passport can satisfy its date checks while the traveller has insufficient Schengen days remaining, or vice versa.