Ironically, a few minutes after posting I received an e-mail describing Flymap UK's system. Which provides the functionality I was trying to describe!
Plan route on a laptop, including NOTAMs and controlled airspace restrictions on a CAA 1:500 000 VFR chart. Then add met data, do W&B and fuel calculations and transfer to USB stick, together with appropriate Pooley's Guide plates. Print off a paper PLOG as back up.
Insert USB stick into aircraft unit and import your flight plan.
It sounds excellent and is surely the way ahead for the 21st century.
The aircraft units include a kneeboard system and a panel mount system; all include a GPS, of course.