It is a lot harder to travel into England from outside of the United Kingdom than it is to travel from England to Scotland or Wales. For one, I do not need a passport to get on a train to Scotland. Nor do I need a visa.

But you most likely have a passport, and most (western/european) countries have "automatic" visas to the UK, so for the most part, training from London to Edinburgh isn't much easier than Paris to London. Sure there is no passport control, but UK passport control is typically just scan your passport's chip and look at a camera.

It's quicker to travel to London from Paris and Calais than it is from parts of Scotland. Even though much of the UK's infrastructure acts as a feeder into London. No, we don't need passports but some people in London seem to have the idea that it's just down the road from us, which it isn't.

If you want to get to Glasgow from Campbelltown it can take you as long as three hours for example, and that's before you hit the motorway. Trying to get from west Sutherland to London is worse. Trying to get there from the Hebrides or Northen Isles even more so.