I live in France for part of the year, but am still a British resident
for all official purposes (tax etc), so don't have a Carte de Sejour.

I want to buy a (2nd hand) French registered car to use and keep in
France. However I am confused about how this works. I called the
local prefecture to ask about this and was told that if I was resident
in UK I could only register a car in UK - not France. Is this true?
I imagine there must be many foreigners driving French cars in France
without getting foreign number plates on them? Can anyone advise me:

- Do you always need to re-register a 2nd hand car when you buy it?
Or only if you will be keeping it in a different departement from
where it was previously registered?

- If I do need to re-register it with the prefecture, will I be able
to do so in France using my British passport? I can provide proof of
address etc in France as required as I have had a house here for
almost a year. Is there any other documentation they will require?

- Are there any other issues I should be aware of, or has anyone else
been in the same position as me & got advice to offer?

Thanks in advance,
Simon.