Strange because according to Eurotunnel website

SWORN STATEMENT OF ABSENCE OF COVID-19 SYMPTOMS AND OF
CONTACT WITH CONFIRMED CASES

This statement must be presented to transportation companies, before boarding, by passengers travelling to
mainland France. It must also be presented to border control authorities.

I needed it to enter France as did all my fellow passengers.

Interesting. That wasn't a requirement on the ET website a month ago and no mention of it by ET at Folkstone or at the French border. All they were interested at French passport control was seeing my T.I.E.. When did you travel?

A declaration "sur l'honneur" is needed to enter France by any route

I travelled by ferry on 28th September. but had previously considered Eurotunnel who I believe incorporate it into the online reservation and do not need to see a paper copy when booking in. However, Frontiere Police may require to see it on entry and in my case it was specifically requested and checked against my passport.

Extract from French Government website (I can't post links yet)

2.2. Health control measures

"If you are already vaccinated, you must present proof of vaccination status and a sworn statement attesting to the absence of symptoms of covid-19 infection and contact with a confirmed case of covid-19".

Ah well, we must have been lucky or it wasn't a requirement at the time we travelled.