The French consulate in London has put this up this morning, so seems to be the first official advice:
From 4 December, fully vaccinated travellers (12 years old or more), and whatever their nationality, have to provide the result of a negative PCR or antigen test (in paper or digital format) carried out less than 48h hours prior to departure. Self-administred tests (NHS test for example) are not considered valid for travel.
uk.ambafrance.org
From 4 December, fully vaccinated travellers (12 years old or more), and whatever their nationality, have to provide the result of a negative PCR or antigen test (in paper or digital format) carried out less than 48h hours prior to departure. Self-administred tests (NHS test for example) are not considered valid for travel.
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COVID-19: rules for travel between France and the UK
Find out about measures in place for all people travelling between France and the UK.