Lets be clear, so far as the UK is concerned, you can go everywhere VFR, or IFR outside CAS.
You may or may not get a service.
There will be days when you wish you had gone airways on top of the weather.
That aside, you can go when you want, how you want, and not talk to anyone the length and breadth of the country. The further north you go the higher you can go; the same is true of the west country.
You can route around every bit of class D if you like and it will not add much to your journey.
Simple really.
The same is true of France except strictly there is no IMC without IFR without an IR without an airways clearance, while in the UK you only need an IMCr and to stay outside class A (and class D unless you have a clearance).