This is my interpretation....
As others have mentioned, VFR over the top is perfectly legal for an FAA PPL ...but also a restricted FAA PPL (issued on basis of JAA licence) who holds a UK IMC rating, as they are no longer restricted to "in sight of the surface". The "in sight of the surface" thing is detailed in the ANO, and as each JAA member country (and the FAA in the FARS) has their own equivalent of the ANO, then these rules apply. For example the French PPL is allowed to fly VFR-Over-the-top as their ANO doesn't restrict them to "in sight of the surface" as far as I can work out.....
So theoretically a UK PPL holder can exercise the privileges of their licence abroad but must comply with either the local ANO or the UK ANO (whichever is more stringent). Now my interpretation of this is that a UK PPL IMC holder, who is excempt from the "in sight of the surface" paragraph of the ANO, can now legally fly VFROTT in France and elsewhere.....
Cheers
EA
