There are 3 levels, Foundation through to Full which come with different privileges. You can achieve a lot with the basic Foundation.
In terms of airborne transmitting - yes the UK is an outlier. It is forbidden to make amateur radio transmissions in the air over the UK, or use a UK licence to do so anywhere I think. The key word here is amateur - so specifically on those bands and with that licence. I think the ISM bands would be fine - and there are balloon projects and clubs in the UK.
I have a Finnish amateur licence in parallel and that doesn't have this restriction but naturally it would still not be allowed to use it to transmit from an aircraft over the UK. And even if it were to be elsewhere there are still some rules surrounding that, and it's hopefully obvious that you need permission of whoever's in charge of the aircraft.
I don't think that's intentionally introduced. My understanding was that mains hum in any grid is an artifact of a noisy signal that just happens to be useful as a forensics fingerprint.
https://www.kccscientific.com/the-dirty-little-secret-about-...