Blimey, that is a lot more complicated than I had first imagined. My husband is forming the opinion that it would be easier to sell the UK registered bikes back in the UK and then buy French registered ones. My only thing against that is my concern about the lack of CT for bikes - so unless you buy new (or know what you are looking at) you could buy a duff one. We are not technically minded - at least not enough to see if we were being sold a lemon. Thanks for all the info, T