Re the IMC rating syllabus, it can be found in LASORS (the UK version of FAR/AIM) Section E:
http://www.caa.co.uk/docs/175/SECTION%20E.pdf
The description of the rating starts on page 12 and appendices A and B which describe the ground training requirements and flight test standards start on pages 20 and 22 respectively.
I would guess private IFR is harder (than the airlines at least). Single pilot IFR in light twins is about as hardcore as it gets I'd have thought.
The issue with IMC rating holders having poor skills is probably about currency more than anything else...with most airfields lacking an IAP people only go flying when the weather is good anyway and have little opportunity to practice approaches (or don't have access to FM immune equipped aircraft).