The French CRIT'air site is now open to register your car if you're visiting Paris. Les Anglais will need a good scan of the V5 - the first inside page, and €4.80 or so for postage to UK. Debit cards only.
Also the VIN number, CO output in G/KM and detailed model of your car
All fairly painless. English web page here:
https://www.certificat-air.gouv.fr/en/ Paris , Lyon, Grenoble