Hello again,
I did it! 
On the 6th of December I flew from North Weald to Cranfield and back, flying between the CTRs on my way there but daring to ask Luton for clearance on my return in the afternoon. I called Luton from above Flitwick, gave position report and route, and expected a detailed clearance through a dozen of VRPs. Instead of that I was treated like a prince, given a VFR clearance through Luton overhead, suggested traffic service after the zone and a telephone-coordinated clearance through Stansted CTA (without asking!) so that I can smoothly glide into North Weald without descending too rapidly
Wow! I want more now
Thank you for all advice, and thank you Luton Radar people if you're reading this.
/h88