Is it possible to use different passports to enter and leave France and the UK?

It is possible for dual citizens to enter/exit countries using the method you have described. 

The rule of thumb when travelling between the two countries you have a passport for is to use the corresponding document for each country when exiting or entering. 

In general, if you are entering a county you are a citizen of, you should show this via a passport/ID card where applicable, which will also minimise any border control issues. 

In your case, you should show your UK passport when entering/exiting the UK, and your French one when entering/exiting France (and when entering/exiting all Schengen Area countries as you

are an EU citizen). 

When travelling to a third country, you should use the same passport when entering and exiting (for example, if you enter Australia on your French passport, also exit on that passport, so

there is a record of you leaving the country). 

It will be increasingly important for dual nationals to follow these rules in the coming years, as both the UK and EU plan to introduce tighter border security rules. 

In the UK, this is the Electronic Travel Authorisation (ETA), already in force for most citizens of countries with visa-free access to the UK, and applying to EU citizens from April 2, 2025.

Read more: New UK travel permit rules: how are travellers from France affected?

In the EU’s Schengen Area, Etias (European Travel Information and Authorisation System) will come into force around six months after the digital border security changes relating to the

Entry/Exit System (EES) begin. 

It is not known when the EES (and by extension Etias) will be implemented, after the systems faced numerous delays.

Read more: Britons, Americans, other non-EU travellers: New problem for digital border checks

Both systems will require non-exempt visitors to register when passing through border control.

UK citizens will be subject to Etias rules but not ETA, and the opposite will apply for French and other EU citizens.

Dual citizens are exempt from registration from both systems (if they hold eligible citizenship), which will be beneficial to minimise pre-journey paperwork and costs relating to the

systems.

However this will only be the case if they show the correct passport upon entry. 

For example, if you showed your French passport when entering the UK after April 2, but did not register for an ETA, you may face issues.