You can certainly be VFR above a solid overcast. This can be done everywhere in the world,
AFAIK.
The problem is whether the pilot's license permits him to fly VFR above a solid overcast. I know of two countries (there may be more) which prohibit this for their own license holders: the UK and South Africa. Nobody else in Europe (
AFAIK) has this restriction.
Such a prohibition is valid worldwide so a UK issued PPL (or a UK issued JAA PPL) holder cannot fly above a solid overcast anywhere in the world. The requirement is that he is in sight of the surface.
For the UK PPL the restriction disappears if the holder has an IMC Rating or an IR, and again this is valid worldwide. (The
IFR privileges of the IMC Rating are valid UK only but that is a separate issue).
So a UK PPL with the IMCR can depart IFR in the UK, climb up through the clouds and provided he is VMC on top by the airspace boundary with France, he can continue that way across France, and then he needs to be able to descend through a large hole in the cloud to land
As Rod1 says, one blade of grass visible through the clouds or whatever is enough to be legal.
Navigation is another matter; obviously UK PPL style dead reckoning won't be much good, but that wasn't the question was it
BTW Rod1 I don't see where the "3000ft" comes into it.