Can I fly VFR on top in France
Nice one. I might make it a little broader and say "weather minima".
How about this:
"JAR-FCL specifies that without an instrument rating you can only fly in VMC conditions. What these conditions are depend on the airspace involved (different classes have different minima, and the minima are different in each country) but the country that issued you your license may specify additional minima.
For a CAA-issued JAR-FCL PPL, there is an additional "surface in sight" restriction, which means that you cannot fly above an OVC (and maybe a BKN???) layer. This restriction is lifted automatically upon acquiring an IMC rating. So even if the IMC rating itself has no legal relevance outside the UK, the fact that your "surface in sight" restriction is now lifted means that you can fly VFR on Top, providing that the country where you fly does not have a restriction in place for the airspace involved.
In practice, it is virtually impossible for the authorities to determine the weather conditions exactly at a certain point in time, and the cases where people were prosecuted because of busting weather minima are few and far between. Common sense prevails mostly. Although incidents such as the one at Blackpool do remind us all that the VMC minimal rules are there for a reason." (Include URL to PPRuNe discussion about G-BBBK or whatever the callsign was?)
Edited: Here's what the ANO says about PPLs:
[A PPL shall not...] unless his licence includes an instrument rating (aeroplane) or an instrument meteorological conditions rating (aeroplanes), fly as pilot in command of such an aeroplane—
(i) on a flight outside controlled airspace when the flight visibility is less than 3 km;
(ii) on a special VFR flight in a control zone in a flight visibility of less than 10 km except on a route or in an aerodrome traffic zone notified for the purpose of this sub-paragraph; or
(iii) out of sight of the surface;
[ANO Schedule 8, Part A, Section 1, subsection 1, para 2c]