I am an instructor, although I don't teach IF...yet.
I believe the Transition Altitude within Class G airspace underneath the Daventry Control Area changed last year to 6000ft (from 3000ft) - see link to AIC: Y 004/2011
http://www.ead.eurocontrol.int/eadba...2011-02-24.pdf
My understanding here is that under the Daventry CTA, below 6000ft AMSL Quadrantal Rule doesn't apply so you can pick an altitude to fly. I am not sure if this applies to all of your trip but would to some of it, and I would have thought should give you the ability to fly IFR above a cloud layer legally (up to 6000ft), where previously QR would force you lower.
I am also interested in this post because I often think about calling up a local civil airfield for a Traffic Service when climbing or decending through cloud to carry out upper air work. However, the RT and workload, and the delay sometimes to call up, then change to Basic Service when above cloud (since it's difficult enough to teach as well as maintain the radio watch that a Traffic Service requires) then back to TS for descent and finally back in touch to reduce back to BS or change to local airfield approach just seems more trouble than it's worth for 500ft of overcast.
When I explain the 'big sky' principle to students I get the impression that they leave thinking 'russion roulette'!
Thats what I thought too after decending recently through a very thin overcast layer after an aerobatic trip to find a hot air balloon of my starboard side, about 0.5nm range with it's canopy poking into the cloud.
Wondering what other people do?