Originally posted by 'Sunday Driver' :
If you are resident in France, you have one month in which to import your UK car and register it with your prefecture.
If you car is of "standard" EU manufacture (ie, not a Japanese/US grey import) then you'll need to sort out the following in order to register your car in France
Fill in the tear-off export declaration slip from your V5C registration document and send it to the DVLA at Swansea. Retain the V5C as you'll need it to register here. If you've any time left on your tax disc, you can send it back as well and request a refund of any expired excise duty.
VAT Paid certificate (quittus fiscal):
Visit your local Hotel des Impots and ask them for a quittus fiscal certificate. You'll need to take along your V5C, original invoice/receipt (though for older cars, they don't usually ask for it) and a utility bill. The certificate is free and incorporates your authority to drive your UK car on its foreign plates for a month whilst you arrange registration.
Type approval (certificat de conformite):
If its a recent car, then it's normal to find a copy of the manufacturer's certificate of conformity inside the owners manual/service book. If its an older car, then you'll need to write to the manufacturer and ask them for one. There's normally a 100-130 euro fee for this although some will issue them for free. Alternatively, you can apply to the DRIRE (Dept of Industry) for an attestation d'identite. Download an application form (with english instructions) from HERE and post it off with a copy of your V5C to your local DRIRE office. They'll check their database of type approved vehicles and post you an attestation certificate. Cost is 67,38 euros.
If your car is 4 years old or more, take it for a CT test. You'll need to change the headlamps for right hand dipping ones (cost up to 200 euros - try a scrapyard). You'll also need to produce your V5C. The CT lasts for 2 years and costs 56,00 euros. Retests on failed items are usually free. The certificate is called a proces-verbal.
Visit your local prefecture and fill in a demande de certificate d'immatriculation. Take it to the counter and hand it over together with your certificat de conformite/attestation d'identite, quittus fiscal, proces-verbal de controle technique, V5C registration document, invoice/receipt, passport and a utility bill. After they've checked everything, you'll be given a slip of paper which you hand in at the caisse together with the fee (credit cards accepted). Fees are based on a sliding scale depending on age of vehicle and its fiscal power rating. You can find a fee chart HERE . Once you've paid, they'll issue you with a new registration document (carte grise).
Now take the carte grise to a cordonniere (key cutting/handbag shop usually situated inside the foyer of a hypermarket) and he'll make you up a set of plaques for about 20 euros. Don't forget to ask him for some rivets - screws are illegal here.
Finally, organise yourself some french insurance cover, stick their green insurance vignette on the inside of your windscreen.
If your car is a "grey" Japanese import, then the process is more complex and costly and outside the scope of this response.