Ah Mr Bond, you are toying with me.
We both know that Schedule 8 of the ANO in relation to the Privileges of the PPL (A) says:-
He shall not:
.......
(c) unless his licence includes an instrument rating (aeroplane) or an instrument meteorological conditions rating (aeroplanes), fly as pilot in command of such an aeroplane:
(i) on a flight outside controlled airspace when the flight visibility is less than
3 km;
(ii) on a special VFR flight in a control zone in a flight visibility of less than 10
km except on a route or in an aerodrome traffic zone notified for the
purpose of this sub-paragraph; or
(iii) out of sight of the surface;
........
(e) unless his licence includes an instrument rating (aeroplane), fly as pilot in command or co-pilot of such an aeroplane flying in Class A, B or C airspace in circumstances which require compliance with the Instrument Flight Rules;
(f) unless his licence includes an instrument rating (aeroplane) or an instrument meteorological conditions rating (aeroplanes), fly as pilot in command or co-pilot of such an aeroplane flying in Class D or E airspace in circumstances which require compliance with the Instrument Flight Rules;
That's taken from the privileges for a UK PPL, the UK CPL privileges include similar restrictions.
As I'm sure you know the privileges of a JAA PPL(A) call up JAR–FCL 1.175 "Circumstances in which an IR(A) is required" which includes
(b) In JAA Member States where national legislation requires flight in accordance with IFR under specified circumstances (e.g. at night), the holder of a pilot licence may fly under IFR, provided that pilot holds a qualification
appropriate to the circumstances, airspace and flight conditions in which the flight is conducted.
National qualifications permitting pilots to fly in accordance with IFR other than in VMC without being the holder of a valid IR(A) shall be restricted to use of the airspace of the State of licence issue only.
It's the proposed abolition of that paragraph from JAR–FCL 1.175 that would kill the UK IMCR.