You either have to have an ICAO ATP exam pass or pass the HPA rating. The HPA rating is a distance learning course and a single exam administered by the training organisation.
Once you have done the HPA rating it covers you for any aircraft that requires an HPA. If you have been flying a piston PA46 and move to a Turbine PA46 you still require the HPA but are exempt the type rating training. The piston PA46 does not require the HPA rating.
A list of SPA aircraft that require the HPA can be found in LASORS and JAR FCL1.
There are only a couple of places that do the HPA rating, one down in Bournemouth whose name I cant remember at the moment.