Brits have been told they will not be allowed to drive across France to homes in other European Union countries.
The warning comes from a Channel Tunnel train operator which claims the move comes following a decision by the French government.
Eurotunnel Le Shuttle, which transports vehicle-carrying trains between Dover and Calais, announced the "urgent update" to passengers on Wednesday.
Non-essential travel from the UK to France has been banned since December 18 in a bid to limit the spread of the Omicron variant of coronavirus, but several exemptions have been in place.
Eurotunnel Le Shuttle issued the update on Wednesday night which stated: "Following a French government decision, on 28/12/2021, unless they hold French residency, British citizens are now considered third country citizens and can no longer transit France by road to reach their country of residence in the EU."
The firm added that it is "unable to answer individual questions regarding the new requirements".
It advised passengers to visit the website of the French embassy in the UK, although its travel information has not been updated since December 20.
No announcement about a change in the rules has been made by the French government.
The UK withdrew from the European Union on January 31 2020, although a transition period was in place until the end of that year.
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