I suspect that it will depend upon the rules of the country in which the aircraft is registered. The ANO applies to any UK aircraft anywhere in the world - although with a proviso that this is subject to any any local law if it over-rides. A local law would not, however, permit a charity flight in a UK registered aircraft.
It would follow that the applicable law will be either that of the country in which the flight takes place or that of the country in which the aircraft is registered assuming it has the same applicability as the ANO.
Where and where then?