Re: Treatment of IFR flight plans (UK, outside Class A)
Ans1: The way it is addressed by whoever submits it into the system. If the FPL is obviously not an "airways" FPL, it will be addressed in the same manner as a VFR plan, with no notification of enroute agencies.
Abroad is a different kettle of fishies. In most cases you can't file IFR without being instrument rated, so the issue never arises. All IFR plans will go via CFMU and you will be expected to follow CFMU compliant (and SRD) routings.
Ans2: See Ans1. No notification of enroute agencies unless you explicitly ask for the relevant address to be included... in which case the aforementioned agency is likely to disregard the plan in any case.