Or at least patch up one hole that's bugging me.

I remember a sci-fi show by the BBC from a few years ago, late 90s if I recall correctly. It was set in Scotland <again, I think> and dealt with an alien invasion. The twist was that the aliens weren't extra terrestrial but rather extra dimensional, entering our 3D space from a 4D existence. Of course, I haven't the slightest idea what it was called.

Any ideas?

Yes! Yes it is! Thank you! ^_^