Just a quick related question as I'm not sure if my memory is playing tricks on me. I'm absolutely not trying to start a political debate.
As far as I can recall UK citizens entering France have always had to show a passport whether we were EU members or not. Is that correct?
There's nothing suddenly new about this requirement from the French authorities?
Yes, UK citizens theoretically had to show identification when crossing the French/UK border because the UK was not in the Schengen agreement, which allows for open borders between members. This also always applied for EU/Non EU citizens entering the UK and ROI. (The ROI agreeed to stay out of the Schengen agreement to preserve an open UK/ROI border)
This used to mean a passport or ID card for EU citizens but I think the UK is now insisting on passports for EU nationals entering the UK.
The big difference is that UK citizens had the right to enter any EU country for up to 90 days, whereas now they have to follow the immigration rules for the point of entry to the EU, and the 27 EU members can set their own rules for third country citizens.