Bringing Northern Ireland Cars to Mainland UK - What Problems Can Occur?

What are the pitfalls and problems with Northern Ireland cars brought to the UK?

I've read various bits of info about buying a car from Northern Ireland and any differences compared to the rest of the UK. It's quite bizarre when the DUP are laying down lines in Brexit talks that they don't want any regulatory differences between NI and the rest of the UK when you find how many differences already exist.

The main issue I've discovered with cars brought from Northern Ireland to England (and Scotland or Wales) is that their MOT history cannot be checked online and more importantly their history is lost when they are given mainland UK registration plates. Any previous history from Northern Ireland seems to be lost so a car with 10 owners in NI that is brought to the UK can effectively lose them.

With GDPR now removing previous owner details from the V5 document it's very easy for unscrupulous dealers to make a car much more attractive than it would otherwise be. A car with many owners can become a 1 or 2 owner car with very little effort.