Neither can the AA helicopters provide a patient transfer service for critical patients since the amount of kit and attendees requires bigger helos than the charities can afford
That is not entirely true as this is dependent on the type of AA aircraft used? I have done numerous patient transfers and once the attendees have been briefed as to what they can and cannot bring, having been made aware of the space available in the back of the aircraft and also the equipment already carried, they have been more than satisfied with the equipment they have been allowed to bring.
It's human nature to bring as much equipment as one possibly can, just in case, on the odd occasion even if we'd have landed in a Chinook for a patient transfer it would have been filled with "critical" personnel and equipment!