From LASORS:
Holders of pilot licences or equivalent privileges for
helicopters (including UK QSP(H) with no previous
SEP aeroplane experience), microlights having
fixed wings and moveable aerodynamic control
surfaces acting in all three dimensions, gliders,
self-sustaining gliders or self launching sailplanes
or gyroplanes, may be credited with 10% of their
total flight time as Pilot-in-Command in such aircraft
up to a maximum of 10 hours towards a JAR-FCL
PPL(A).
The problem of modern high-end microlights such as the C42 is that their existence was never considered in the early years of microlighting when most microlights looked and performed like an illicit affaire between a tent and a lawn trimmer. Whilst aircraft such as the C42 do indeed have excellent performance, the simple fact is that a line has to be drawn somewhere. If the C42 was registered and operated as a SEP Class aeroplane, hours flown would count in full towards any JAR-FCL aeroplane pilot licence - but if the CAA were to accept hours flown on a G-M*** registered C42, then someone would want hours on something less capable accepted, and so on ad infinitum.
As has often been said, make too much of a song and dance about how much 'better' a C42 performs than an aged spam can and someone might then say "In which case you will be regulated in the same way as an aged old spam can" - and no-one really wants to visit that on the BMAA or its members!