You may have problems if you don't have the small polish logbook, I have just registered 2 polish 126s I had them MOTd locally on the VIN and sent the paperwork off with the MOT - I phoned DVLC and they said I had to send the polish Logbook to prove its age, without it they wouldn't register it, I think the guy was just being a pain, I also had problems getting the one 1999 fiat through an MOT on emissions, what year is your fiat ? Your best bet is to phone DVLA Swansea Direct - some of them are helpful at DVLA - worse case scenario DVLA may want to physically inspect the fiat to ascertain the year it was made, I had to do this with a split screen camper I imported a few years ago, trailered it 50 miles for them to inspect, they looked at it for ten seconds - to check the chassis and engine numbers and all sorted!