Once you take it over for more than 6 months you need to get a registered in the French system. Much hassle. Less than 6 months, you don't need to do anything.
I wouldn't bother , ive had cars in France still registered and insured since 2003 , never been a problem . Bring them back to uk keep MOT up to date then stored in France for a year !
edit to add : A friend went through this process of re registering his van ( Renault ) it was a right pain in the arse took several months of chasing paperwork.
I have also scrapped a transit in France , I could have left it like a lot of "Poles" do and leave it by the side of the raod I decided to do it legally I submitted the correct paperwork inculding V5 , passport , Drivers license , Internation license , insurance ,etc. and it took over a week to get the signatures , then send French pasperwork back to DVLA to register the vehicle as scrapped .
The French Buracracy system is total bulls
t , also be aware if you send money over to France above 4000 Euros the bank will " sit on it for a month before you have access to it , Its a total s
te state of affairs and its going to get worse , " Quote that little French B'stard Sarkozy ...Zer are too many foreigners in France "
One of the many reasons I am leaving