The UK is categorised as "amber", which means the negative COVID-19 must be:
The French Government travel PDF gives full details, and we've included the (translated) table that applies to travel from the UK below.

Travellers aged 11 and under are not required to take a COVID-19 test. The test can be a PCR or antigenic/LFT test. You'll show your QR code result or negative certificate at the border. It's still required to be fully vaccinated to enter the country, but keep in mind: No Longer "Fully Vaccinated" After 7 Months In France, Boosters Required For Travel Starting In 2022.
The test you will need is the "Lateral Flow Antigen Fit to Fly Test Kit" which is available from Project Screen for just £19 each.
Click here to order your fit to fly France entry tests >>>