I can't remember the minima for horizontal and vertical separation from cloud... Chilli is probably correct for all practical purposes. If you want to do this, get an IMC or an IR.
A PPL/IR is not a mystical rating that involves complex rituals and scrawling pentagrams in the sand ! - it can be done for a lot less money than you think, on a single, and will improve your flying no end. I'm surprised more people don't go for it, especially the regular flyers.
(Edit - if you have an IMC, mate.. what's the problem ? As for 12g... I avoid convective build-ups by 10 miles in a 767.... your call !)