Originally Posted by
catandmouse
There are no checks on the land border between France and Switzerland (or only very rarely).
The Swiss Federal Council today announced the end of tests to enter the country from fully vaccinated people, as from 22 January.
In France you need to have the dreaded "Déclaration sur l'honneur", though I've never been asked to show it at the border or elsewhere.
Coming from the UK, the OP would be expected to have a PCR or antigen test of less than 24 hrs to enter France. The odds of being checked are indeed low but, if it were me, I would do an antigen test pre-departure for peace of mind.