The East Anglian Air Ambulance and royal aides have rushed to Prince William's defence after his part-time job as a helicopter pilot and attendance at only two royal engagements this year came under attack.
The Duke of Cambridge has come under scrutiny for what some have regarded as his reluctance to take on more official duties. William averages 80 hours per month – or 20 hours per week – as a pilot, taking part in a four days on, four days off rota, which averages 8.5 hours per shift.
Palace sources claimed that Civil Aviation Authority rules on rest periods mean that William is banned from doing any sort of work on some of his rest days, including carrying out royal engagements.
But the Civil Aviation Authority (CAA) said the Duke's staff were "confused". "It's true that you can only work a certain number of hours in a given period, but to suggest that pilots can't do anything else on some rest days is totally unenforceable," a spokesperson confirmed.
"When they are having rest days, their time is their own, and they can do what they want, including carrying out royal duties. We check pilots' shift patterns and the Duke is fully complying with CAA rules within the rota he is working, so his days off are his own."
A palace source responded by telling HELLO!: "Over the course of the year, the monthly average would be 80 hours on shift. His royal and charitable duties are on top of that.
"There are engagements and tours and meeting and all sorts, and his team works with the Air Ambulance Service to fit it into his diary. This is no different to what he's been doing since he started flying. It's ultimately a very skilled and rewarding job - he's flying doctors around to help save people's lives."
A Kensington Palace spokesperson added: "The Duke is incredibly grateful to have the opportunity to carry out his skilled work with the East Anglian Air Ambulance. It is a great opportunity to connect directly with the community and he considers it very rewarding to be part of a team that provides such a valuable, and often life-saving, public service."
East Anglian Air Ambulance had its annual meeting on Saturday, when a spokesman for the charity said the prince was "very much part of the team", and was doing "a very important job".