A lot of the car dealers in the North buy their cars in the UK and bring them over. You would be getting a UK car anyway, you will know by the number plate most of the time. They can get a car delivered cheaper than the normal person from the UK and they can factor in their cost of going over to England across a number of cars, (if they even go over at all, a lot of hem have a dealer in England who they know who buy the car for them)If you go to the UK you get more of a selection and a cheaper price but you have to factor in the cost of bring it back and if you cant find what you want you come back empty handed.
I wouldn’t like to buy a car that has been always been in the north with high miles as the roads have gone so bad that there would probably be suspension issues. UK cars with high mile have mostly motorway driving and this is fine in my view. If you keep an eye on Autotrader you will find a good selection of cars in the north and you can negotiate a good discount with them