BB,
I have never seen the need nor had the desire to fly IMC outside Controlled Airspace
Then you have led a more sheltered career than you previously thought. There are some large gaps in the UK LARS system, more so since the military drawdown over the past decade or so.
In such areas, you might get flight following via the excellent London and Scottish Information service, but that is all.
Unfortunately, the UK system works on the basis of "contracted out, must make a profit, safety comes second to commercial interests (whatever the authorities might wish to say). Liability issues mean that ATC controllers don't wish to take on a service they aren't mandated to provide.
So outside CAS is the responsibility of the operator (read captain)!