In reply to Andy Manthorpe:
I was surprised by your question but looking online confirms it.
This -
At French border control your passport may be stamped on entry and exit. You should also be prepared to:
Queue in separate lanes from EU, EEA or Swiss citizens.
Show proof of where you intend to stay, for example, a booking confirmation or proof of address if visiting your own property (e.g. second home). Further information is detailed below.
Show proof of insurance for your trip. Please check the guidance on travel insurance here.
Show a return or onward ticket
Prove that you have enough money for the duration of your stay. Further information is detailed below.
France categorises possible accommodation arrangements for visitors as follows:
Staying with family, friends or third party - you may be asked to provide an ’attestation d’accueil’ (welcome invitation) from your host if you are staying with friends or family. The French resident hosting you will need to obtain this attestation d’accueil from their local Mayor’s office, and send the original attestation before you enter France. You should also be prepared to show proof of funds of at least €32.50 per day, for the duration of your stay. If you do not have an ‘attestation d’accueil’ you should be ready to fulfil the requirements of option 4 below.
You have a second home in France - you will need to be able to prove ownership or tenancy of your property e.g. a tax or utility bill.
You are staying in a hotel or other commercially provided accommodation - you may be asked for confirmation of your reservation when entering France. You should also be prepared to show proof of funds of at least €65 per day for the duration of your stay.
You do not have an ‘attestation d’accueil’ or any pre-booked accommodation - in this instance, you may be asked to prove you have sufficient means for your visit, of at least €120 per day for the duration of your stay.
is from https://www.gov.uk/foreign-travel-advice/france/entry-requirements.
From what SD says it does not appear to be enforced, but it clearly is a possibility.
Dave