As far as I read it and i am sure someone else can clarify. the Idea of the enroute IFR is that you take off VFR/VMC fly on top to detonation where your approach and landing is VFR/VMC.
The problem with that as an example is you cannot fly a STAR and as such would have to leave CAS before the start of the Star.
Somewhere like Barcelona you may well indeed get CAVOK but 30 miles inland there could be heavy build ups over the mountains at start of STAR where you have to leave and are on your own.
The other problem I have is enroute in a single you may be over airports below where the cloud base is 200 feet what happens if you need to divert!
As I read it you can with a UK IMCR Leave the UK in IMC and return in IMC but only in UK airspace.
Pace