Interesting question from someone so far away.
Overview - 22 HEMS Charities or Commissioning Ambulance Service.
Depending on whether you include reserve aircraft there are around 43 aircraft dedicated to HEMS/Air Ambulance.
I will include all aircraft types, not just Leonard or SAS aircraft.
Operators involved:-
1. Babcock
2. Specialist Aviation Services
3. Sloane
4. GAMA
5. Heli services International (HSI)
Those Air Ambulances with their own AOC:-
1. Devon Air Ambulance
2. London’s Air Ambulance
3. Yorkshire Air Ambulance
13 x H135
12 x H145
9 x AW169
4 x MD902
2 x AS365
2 x AW109
1 x Bell 429
Air Ambulance Northern Ireland - 1 x H135
Cornwall Air Ambulance Trust. - 1 x AW169, 1 x MD902
Devon Air Ambulance Trust - 1 x H145, 1 x H135
Dorset Air Ambulance. - 1 x AW169
East Anglian Air Ambulance - 2 x H145
Essex & Herts Air Ambulance Trust - 1 x AW169, 1 x MD902
Great North Air Ambulance - 2 x AS365
Great West Air Ambulance - 1 x H135
Hampshire & Isle of Wight Air Ambulance - 1 x H135
Kent Surrey Sussex Air Ambulance - 2 x AW169
Lincolnshire & Nottinghamshire Air Ambulance. - 1 x AW169
London’s Air Ambulance - 2 x MD902
Magpas - 1 x AW169
Midlands Air Ambulance Charity - 1 x H145, 2 x H135
North West Air Ambulance - 3 x H135
Scotlands Charity Air Ambulance. - 2 x H135
Scottish Ambulance Service. - 2 x H145
The Air Ambulance Service - 2 x AW109
The Children’s Air Ambulance - 2 x AW169 (Inter hospital transfers, not primary HEMS)
Thames Valley Air Ambulance. - 1 x H135
Welsh Air Ambulance Charitable Trust - 3 x H145, 1 x H135
Yorkshire Air Ambulance. - 2 x H145
Not a UK organisation, but there is an Irish Community Air Ambulance, which is a Sloane AW109.
I hope that helps.