Gertrude the Wombat
There is widespread belief, possibly correct, that IFR outside the airways system is not permitted in France. I was told this personally by a French ATCO. I don't what about anywhere else, though Spain would be interesting.
Someday, somebody, will come up with an authoritative list of what is allowed in which country. I've never seen such info anywhere, despite it being an often asked question. Somebody has to know because plenty of people fly little planes IFR all over Europe on business. The problem is that the community of "IFR" contributors here on pprune who know the nooks and crannies of this stuff is very small. Or perhaps if somebody knows, they are keen to keep it quiet. Why? No idea.
It's interesting to note than an FAA PPL/IR (is it possible to be a JAR PPL with an FAA IR?) can fly a G-reg IFR outside CAS (F/G) in the UK. If France/Spain allowed the same, that would be great because despite the prevalence of Class E in France/Spain, it is possible to fly usefully there in F/G. It would be a good option for European touring because for most non-owners, N-reg is not feasible.
I doubt it is possible because it would be an "easy IR" - using the FAA IR as a back door to a "proper" IR is exactly what the JAA states are keen to prevent.