If you are going for a polar orbit (ie. circling from one pole to the other), any initial speed you pick up from the rotation of the earth will need to be cancelled out by burning fuel.

So the further north (or south) you go, the lower that speed is (since you are closer to the rotation axis).

If you’re going for an equatorial orbit, that initial speed is helping you, so you maximise it by launching as far away from the axis as possible (ie. somewhere close to the equator).

It makes me wonder whether there is any place further north than Sutherland where the ESA could set up (or has already set up).

I don‘t know why nobody is mentioning it, but Esrange[1] in Kiruna is an active European launch site, arguably far more North than Sutherland. Even though launcher activities seem to be limited to sounding/sub-orbital rockets at the moment, I don‘t see a reason why they should be restricted to it.

[1] https://en.wikipedia.org/wiki/Esrange

Why not Svalbard.

Svalbard is a bit tricky - while it is part of Norway (which itself is part of the ESA), it has military restrictions, and other countries can operate commercially from there.

There is a (suborbital) rocket launch facility there to study aurora etc, but it's limited to 4 launches per year.

Greenland could be a good site -- I believe they are still a member of ESA through Denmark, so Qaanaaq would be a great place for polar launches, weather and access permitting.

Sun-Synchronous orbits. Earth observing satellites like them, they're good when launched from high altitude, and a lot of the newspace smallsat market is in earth-obs with modern optics and processing.

A sun-sync orbit keeps the satellite in the sun (out of Earth's shadow) and typically peels a whole pass of the planet every few days, IIRC.

(also Polar orbits, but there are fewer of those)

It has a weather hole that gives it more clear days then other places.