Prince Charles has been criticised for flying 200 kilometres in a private helicopter to speak to climate scientists about reducing aircraft emissions.
The prince's flight from Highgrove to Cambridge was estimated to produce 2.5 tonnes of carbon emissions and cost £12,000 (NZD$24,500).
The 71-year-old told Cambridge University researchers developing a zero-carbon flight that they needed to "act quickly to rescue this poor old planet".
Experts report Prince Charles could have cut emissions to an estimated 0.2 tonnes had he travelled by private car rather than the Queen's helicopter.
Republic campaign group chief executive Graham Smith said the royal "wants to play the role, but not walk the walk".
"His view seems to be that it's one rule for him and one rule for the rest of us."
Clarence House defended Prince Charles in a statement saying carbon emissions from his travels were offset each year.
"The prince is not personally involved in decisions around his transportation arrangements," a spokesperson said.
"They are made based on what is possible within the constraints of time, distance and security."
Prince Charles was recently criticised for flying 25,000 kilometres in private planes days before the World Economic Forum.