Oh, like the Pegasus air-launch system. Works fine, but not a huge win on cost.
I'm surprised that anyone wants to launch from that far north. Most launch sites are further south, so you get more velocity from the earth's rotation.
I think the main win is flexibility, you don't need as much infrastructure at your "spaceport". The payload is small so the fuel savings from launching closer to the equator would be minimal, especially for higher inclination orbits. Plus it's an easy political win to do the launches locally (the UK's plan calls for spaceport in Scotland, England, and Wales. I suppose that's their equivalent of NASA projects being built in all 50 states to spread the pork around). Plus doing launches in overseas colonies/possessions can be politically fraught. It occasionally has been an issue in France
There are more costs than just the launch itself though. The UK has a pretty big space industry. Lots of satellites and satellite components are made here. Not needing to ship your payload to Kazakstan probably saves a few quid if you're building a lot of it in the UK, and the reduced risk of it being damaged in transit will help significantly.
> I'm surprised that anyone wants to launch from that far north. Most launch sites are further south, so you get more velocity from the earth's rotation.
The reason is that Scotland and northerly launch sites favour launches into polar orbits.
There's been talk of a spaceport in Scotland as well (possibly a competing bid to this). The touted benefit of being further North was easier launches into polar orbits.
I'm surprised that anyone wants to launch from that far north. Most launch sites are further south, so you get more velocity from the earth's rotation.