Green eyes, you cant have data to prove there is no evidence!!! Please PM me the data you claim to have and I would be happy to critique it. Manchester University did the definitive audit of HEMS and concluded the only lives saved are isolated head injuries where the helicopter carries a doctor and no doctor could be otherwise delivered. At the time it was 1-2 cases per year within the M25, now with rapid intervention units it is even less.
Sadly your comments about brain injury and heart attacks sound logical but heart attacks are stabilized as well by paramedics in the field as by doctors. Intervention occurs in hospital and the therapeutic time window is either not improved or is not an issue in these cases.
Anyhow, as you say it is about police helicopters. I was merely making the point that necessity is hard to define and may be more relevant to whether the individual has to pay for it or not!