I don't know if borders matter much in this case. It's approximately just as easy to travel to England from many other countries as it is to travel to England from the rest of the UK.
LOL, no that's simply not true.
The borders between Scotland, England, and Wales are effectively like state borders in the US. Unless you see a street sign, you wouldn't know you crossed it.
NI is physically on a different island, so requires a boat or plane ride.
And all of the UK (ignoring the territories and ex-colonies) is on islands. And require a valid passport, passing through customs/immigration checks, and either a plane, boat, or train ride.
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.
What? No it's not just as easy, especially since Brexit now there are real border issues compared to driving down the road.
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.