As long as it's on a trailer you don't need a grey card or french MOT, either in France or here.
You can get an letter of authentication from Citroen UK at Slough to send to DVLA with all the other paperwork and MOT, you may also have to take the car to DVLA for them to authenticate it themselves - ie chassis, engine number etc match (we did). Not hard though just a little time consuming.

what if you put it on a replacement chassis with a new engine

then you transfer the chassis number and engine number.

If the car's legally on the road over there, drive it home insuring it on the chassis number, not the registration number.

When you're over here with it, MOT it, then go to the DVLA with all the paperwork, and they will charge you some money and give you a registration number and V5 for it.

Neil's the man to speak to.

Have you got a car you want to bring back?

We've done it twice, once with paperwork, once without it's really not hard.

That's a little simplistic if you don't mind me saying...that is just what DVLA will be checking for they will only authenticate a genuine car.

The DVLA are more likely to spaz out and play hardball if you turn up in a car with no chassis number or engine number aren't they?

They're only likely to want to see it if you have no paperwork, if you poll up with no paperwork, and mismatching numbers why would they give you a registration number to drive on UK roads?
Also to get an age related plate rather than the dreaded 'Q' you will need a letter from Citroen UK at Slough, you have to give them the engine number and chassis number on the car, they then give you abuild date from their archive so both must be from the same car, and still be present and un-messed with when seen at DVLA - again this only applied if you have no original paperwork.

They were a nightmare to deal with when i was trying to register the Acadiane. I supplied them with The engine & Chassis numbers & even pictures of the van & even gave them the build date according to the ORGA number. I later had a phone call asking if i was sure that it was a Citroen as they didn't have any records!

I think the problem stems from the fact that the guy Mr. Page who most people used to deal with has since left & now whoever's in charge doesn't have a scooby or has no interest.

In the end i contacted Pete Abbot & he typed me out a dating letter on 2CVGB headed paper & that was enough to satisfy the local DLVA office.

If there's no paperwork then there's no numbers to match the car?

If there's no numbers on the car then how can the paperwork not match? I don't understand why you'd go through any hassle anyway, I'd just refit the chassis and engine numbers if I'd changed the engine and chassis. I can't be arsed with dealing with any grief over non matching numbers just because I'd stuck another engine in or rebuilt it on a new chassis.