The salient point, is that medical supplies and services are VAT exempt and therefore, VAT on goods purchased cannot be reclaimed. Charities can register for VAT depending on the nature of their supples.
Where a commercial operator operates the air ambulance on behalf of a charity, do they invoice their costs to the charity including VAT? Or is there an exemption certificate?
The above link covers only part of the minefield that is VAT and is not easy to summarise and it's already written in a faitly succinct form.
I could see this being very difficult to administer given the differing setups involved.
Cheers
Whirls