JECUK you are confusing TYPE rating with CLASS rating. A type rating is required for things like B737s, a class rating, which is likely what you mean, is, e.g. SEP(L), i.e. single engine piston (land); IOW needed to fly Cessnas, Pipers, etc.
If you wish to convert your ICAO PPL license to a UK issued JAR PPL license by sitting two exams (air law and human factors), you need to satisfy several experience requirements, LASORS refers (IIRC 100 or 150 hours PIC, x-country time, etc). You will also need a valid JAR/CAA medical.
Understood, I was referring (badly!) to the Credits section of LASORS C1.3 where it says if no valid aeroplane rating has been held for a period of 5 years then all exams must be completed.
My take is that for an Australian licence, if the licence has not been taken away, its aeroplane rating is always valid.