I was wondering how practical it is to combine hems and pas given that the required funding would be less?
Well, for some Police Units (Wilts, Sussex) it is obviously very practical. For others (most of the metropolitan forces for example), it is almost (but not totally), impractical. The network of 'publicly funded' air ambulance cover is increasing all the time and so the need for police air support units to carry out this type of task is decreasing.
Note. I appreciate that all the 'pure' air ambulance operations in England and Wales are funded by charity. Generally the contributors to that charity are the public, hence 'publicly fuded'. Think of it as voluntary directly targetted taxation!