Be aware that the CAA has changed the
advice on its site since Ajay took his screen shot. It now no longer suggests that the foreign IR gives the same privileges as an IMC rating.
Nevertheless, the results of Ajay's enquiries are interesting with regards to flying a G-reg in France and Germany -- it appears that an FAA (or other ICAO) licence can be used to the same extent as if as if the pilot were flying over the UK.