Nigel,
You seem intent on ignoring answers on other threads and misinterpreting what has been said in reply to your posts.
From the first thread where you advocated punching up into IFR instead of scud running to the latest of deliberately flying into cloud in an uncertificated helicopter for experience, the main argument against what you are advocating has been that there exists a system for flight under IFR which encompasses: airspace requirements, equipment, training and operational procedures - with a qualified helicopter.
In the first thread, after you introduced the subject of single engine helicopters, you were informed that ICAO Annex 6 Part III had been amended to include the Standards and Recommended Procedures (SARPs) for SEIMC (Section II Chapter 3.4 and Appendix 2). There is no international barrier to controlled access to IFR by adequately qualified singles!
The difficulty of flying in cloud relates to instrument flying skills (the currency of which degrades faster than any other) which is directly related to the stability of the helicopter and its handling qualities. These aspects of flying are not related to the number of engines and that has never been an issue.
You have now moved the discussion to this thread and re-introduced the subject of the number of engines. Flying in singles is adequately addressed in State's Operational Rules (I would question JTobias' suggestion that you can 'get in a single and fly between skyscrapers in New York'; Part 91.119(a) appears to preclude that practice) and doesn't enter into this discussion.
All of those who routinely fly IFR will tell you that the first encounter with IMC on a departure at night when close to T/O minima - after a summer where little low cloud has been encountered - is a spine chilling event.
Control can be lost extremely quickly in an unstabilised helicopter once the visual cues are degraded; flying in cloud is almost always associated with some degree of turbulence and no visual cues. To advocate deliberately doing this - even with an experienced pilot on board - in an unstabilised platform is exposing both crew members to a risk that is unwarranted.
Jim