Given that Great Britain is an island, it is still much easier to drive down the M6/A74(M) or take a hike around the Welsh borders than say, take a flight or swim.

It can be quicker to reach southern England from continental Europe than from Northern Ireland or many parts of Scotland. Or the Isle of Man (which I'm well aware is a Crown Dependency.)

The UK consists of a number of islands. We have hundreds in Scotland with tens of thousands of people living on the other ones. England and Wales have significant ones such as the Isle of Wight, Ynys Môn and Lindisfarne. The IOW has at least 100,000 on it.