Interesting question, 1261.. .. .The fundamental premise of class E airspace (and in particular, of having mostly class E airspace at lower levels as in Germany or the USA) is that IFR and VFR traffic can avoid each other visually in VMC with sufficient reliability to fly safely.. .. .If you don't believe they can, you end up with positive control and a system of aispace with much class A/B/C and the rest class G as in the UK. Class E is pointless. . .. .The choice between A and B/C is presumably made on the basis that some airspace is sufficiently busy that even entertaining a request from a VFR aircraft wanting to cross the airpsace is sufficiently disruptive as to be inconvenient or dangerous. More likely in the UK, the vast tracts of class A we have are allocated on a systematic or historical basis, rather than a case by case evaulation of the impact of allowing VFR aircraft access to the airspace.