The King will have to stop speaking out about some of the causes closest to his heart if Nigel Farage wins the next general election, according to multiple sources.

As Labour leadership rivals circle Sir Keir Starmer after poor local election results and the monarch faces the prospect of a fourth prime minister in his four years on the throne, insiders have revealed that the possibility of Farage in Downing Street is the source of more concern at the palace.

Charles’s record as a prominent environmentalist has helped successive governments cement Britain’s position as a world leader in the fight against climate change. The expectation is that under a Reform UK government, the King would be less able to speak out on these issues, despite the party’s apparent pro-monarchy stance. It has vowed, for example, to make all state-funded schools in England display a portrait of the King and fly a Union flag.

Palace insiders, constitutional experts and royal biographers have suggested that the arrival of Farage in Downing Street would curb the monarch’s ability to publicly support the UK’s push to reach net zero on carbon emissions, as well as the many other environmental causes he has championed for more than half a century.