In the UK, and in N Europe in general, if you are VFR outside controlled airspace (which means Class E,F,G) then you can fly anywhere you like - obviously avoiding danger, restricted, prohibited areas etc of which there are plenty of especially in some countries.
You must always get enroute and airport notams. Use the NATS narrow route briefing option.
In S Europe things can be very different e.g. prescribed routings even for VFR.