Eurocontrol routes can be filed around France down to FL070, generally.
It is the only place in Europe where you can do that (I think Germany may be similar but it's a long time since I flew VFR there) - thanks to their extensive Class E airspace segments, generally FL065-FL120, above which it is Class D.
It is the transition between that and other countries' airspace where the issue occurs.
Class E? You would need to find the money to pay a whole load more ATCOs to cover IFR traffic in that, which isn't going to happen in the UK
