Is it allowed or not? VFR en-route is not allowed but what does this actually mean? Hmmmm, confusing!

Yes it is allowed and, in the UK's case, I would guess is designed to give mil aircrews freedom to operate. Is it well used? Well it wasn't the last time I looked and I'd have to guess that the crews don't understand the change. VFR en-route is,as you say, not allowed. But why would you want to at those levels?

Don't know about UK,but in Europe VFR in class C not allowed above FL195, unless you have special permission,which I think only military can get...