This has been discussed here and elsewhere, and GASIL is as wrong as is possible to establish.
The IMC Rating is valid UK only, but when you do it you also obtain an exemption from the CAA PPL requirement to be in sight of the surface.
The ICAO PPL has no such requirement, so when you do the IMC Rating, you can fly out of sight of the surface worldwide. The removal of the requirement does not have territorial restrictions.
Another country might restrict a PPL to be in sight of the surface, in which case you have to obey that. But France doesn't.
I have it in writing from the CAA, too, and there isn't a whole lot more than one can do than that!