Scotland's probably OK too

But look, how can this be a business? If there are no "barriers" to overcome (e.g. buying elsewhere in the same country even if it means a ferry-ride), then anyone can do it for themselves, at less cost than your costs plus your mark up. If there are barriers (type approval being one) then you need to do the research.
The 'old trick' of ordering a UK spec car from an EU source for delivery in the EU to be brought back as a 'personal import' has been scuppered by movement in exchange rates.
This is a highly capital-intensive business (unless it's cash deals with a scallywag) and seems a non-starter.
Now, exporting bashed up / written off old Mercs and Peugeots to Africa .... that's another story, and only one that needs reading if you can do something with the non-convertible African currency!
Move on, the numbers don't make sense.