EMS is still classed as Commercial Air Transport, so the aircraft has to operate to the appropriate performance standard for it's seating capacity. Generally this would require PC2. The other factor most relevant, is the operating environment: is it non-hostile non-congested, non-hostile congested, hostile non-congested or hostile congetsed? Generally a HEMS operation could expect to encounter at least two of those combinations during its operations, and that would also determine the performance standard expected.
You've got to be kidding! Picking up a patient in a congested area and they still are required to conform to PC2??
I'm sure that I have seen photos of the London HEMS aircraft sitting at a roundabout in the middle of a road somewhere with wires and houses all around. I suppose the EC135 or AS365 is more powerful than I thought.
Commercial Air Transport should be for fare paying passengers - not patients whose mode of transport has been decided by a medical professionals (doctors or paramedics).