Note that the bases of UK controlled airspace step down in stages as you progress west, ultimately reaching a lower level of 2500ft in the Haverhill area and just south of Duxford (you CANNOT go over the top as there is Class A airspace above!). This an infringement hotspot area, and there have been great efforts between NATS and Duxford to eliminate these. I suggest you contact Duxford for a briefing before you set off and certainly before you leave to come home. Also be aware of the Transponder Mandatory Zone around Stansted CTA/CTR
Also, plan on going around rather than through the Stansted CTA/CTR if you approach from the CLN area as they are likely to refuse transits if there is a large volume of traffic for Duxford.
I'm not aware of any no-fly areas for VFR across the North Sea on that route, other than the danger areas around oil rigs.
Enjoy the trip!