Hello!
...or Airline Captain stories.
That was me with this story and not the guy you repiled to, but it dosen't really matter. I think this story about „my“ airline captain is not such a bad analogy to the IMCr outside the UK: This guy has a valid instrument rating and was flying in a perfectly safe way, but his rating did not apply to the type of aircraft he was flying. Therefore he was prosecuted. The holder of IMCr rating is flying perfectly safe too, but outside the UK his rating is unknown and therefore nonexistent. Therefore he will be prosecuted if he gets caught using it. Simply put (see bolow).
For flying abroad (wordwide!), there is a very simple basic rule that applies to private and commercial pilots/operations: You must comply with the more stringent/restrictive set of rules between your national legislation/privileges and those of the country overflown.
For example: In Germany, flying VFR on top of an overcast is perfectly legal with a private pilots license, provided the ascent above and the descent below the clouds can be performed according to the visual flight rules and the aircraft is equipped for radio navigation. If a "normal" UK PPL does not allow this, then the UK PPL holder can not fly VFR on top in Germany. His more restrictive national rule overrides the foreign one. But if he is allowed to do so with UK PPL & IMCr, then he can also do it in Germany because he complies with national and foreign rules, even if the IMCr itself is nonexistent in Germany.
On the other hand, there is no such thing as instrument flying outside controlled airspace in Germany. Therefore, all other possible uses of the IMCr are banned by foreign rules, because an instrument rating is required for flying IFR _within_ controlled airspace. Simple, isn't it?
Happy landings,
max