Maybe you are in the wrong forum? We do everything upsidedown here. We don't have a UK style NPPL - but we could certainly use one. No stoopid OTT CASA medicals for a start!
For what its worth to you, you can get the upsiide down VMC definition from our Aussie AIP. Basically in uncontrolled airspace, under 10.000 ft, we need 5000m vis and be 1500m horizontally and 1000 ft vertically from cloud. VFR may only be conducted in VMC, OR below 2000ft agl by being able to navigate by visual reference to the ground or water. (Interesting how aviation mixes metric and imperial units in one sentence dont you think?)
Gawd knows what it is in UK, guess they would call 10,000 FL100 for a start but probably close. I think the UK thing has something about in sight of the ground and clear of cloud - or something.