Some thoughts on the differences between the arrangements of airspace in the US and UK.
In the US, the ethereal airspace is class E, which controls IFR flights, but does not control VFR flights. Above FL180, airspace becomes class A but then who would want to be doing VFR there anyway. Local airspace around major airports is class B, secondary airports class C and smaller airports class D.
In the UK, the ethereal airspace is class G, which is totally uncontrolled. I'm not sure what's above FL245, but it's probably class A. Class A airspace is all around low altitudes to encompass all airways as well as many areas. Airspace around all reasonably busy airports that aren't LHR is class D.
UK airspace is simpler in that it uses less classes. Essentially there is two completely opposite varieties, class A and class G, with class D to allow the use of airports wthat aren't LHR by VFR aircraft. In this way, scheduled flights and GA flights are kept out of each others way. Scheduled flights can do their thing without having to worry about pesky GA, and GA flights can do whatever they want without any need to submit to the air traffic services.
Of course, US airspace is more mixed allowing more freedom for GA and not constricting scheduled flights set regions. Of course, because GA operates in class E airspace, they have more control by the air traffic services, which doesn't happen in the UK probably because NATS can't be arsed.