You see why I restricted by last post to the holder of a UK (not JAA) PPL!
What JAR-FCL 1.175(a) states is that:
The holder of a pilot licence (A) shall not act in any capacity as a pilot of an aeroplane under Instrument Flight Rules (IFR), except as a pilot undergoing skill testing or dual training, unless the holder has an instrument rating (IR(A)) appropriate to the category of aircraft issued in accordance with JAR–FCL.
This is modified by JAR-FCL 1.175(b) to take account of the fact that, in the UK, one may not fly under VFR at night. The easement from holding an IR, however, relates only to flight at night and the ban on IFR by day in JAR-FCL 1.175(a) is unaffected.
JAR-FCL 1.175(b) goes on to allow for the privileges of the UK IMC rating to be exercised, but only in UK airspace. This ties in with the ANO, Section 2, para. 2(c), which allows the holder of an IMC rating to fly under IFR in Class D or E airspace.
To summarise all of this, the holder of a JAA PPL may not fly IFR in any airspace (JAR-FCL 1.175(a)) except:
1. At night, provided a night qualification is held (JAR-FCL 1.175(b))
2. In any airspace provided an instrument rating is held (JAR-FCL 1.175(a))
3. In UK Class D, E, F or G airspace provided an IMC rating is held (JAR-FCL 1.175(b)) and ANO, Section 2, para. 2(c)
To clarify the bit about flying above cloud, the requirements for a PPL holder without an IR or IMC rating, are:
1. To maintain VMC (Rule 25 or 26 as appropriate)
2. To be in sight of the surface (ANO Schedule 8)
To comply with 1. - If above 300ft AMSL maintain 5km or 8km flight visibility and 1500m horizontal/1000ft vertical separation from cloud. If below 3000ft, maintain the appropriate flight visibility, clear of cloud and in sight of the surface.
It is worth bearing in mind that JARs are Requirements and not Regulations. They are only enforceable in the UK provided that they are allowed for in UK legislation (e.g. the reference in the ANO, Schedule 8 to JAR-FCL 1.175). The legislation concerning aviation in the UK is contained mainly in the The Air Navigation Order 2000, The Rules of the Air Regulations 1996 and, oddly enough, the Railways and Transport Safety Act 2003 and it is here that one should look for the definitive position. Unfortunatel, as with anything put together by the legal profession, much of the content of the ANO is quite unintelligible!