Prince Harry and other royals who “feed the progressive agenda” are signing the British monarchy’s death warrant, the head of Britain’s oldest conservative think tank cautioned.

Speaking on Breitbart News Daily, Bow Group chief Ben Harris-Quinney praised Queen Elizabeth II for remaining strictly neutral on political matters, but warned that her heirs are showing less respect for the convention.

“The Royal family is supposed to be apolitical, but what we’ve seen in recent years is the Duchess of Cambridge editing left-wing blog the Huffington Post,” he told SiriusXM host and Breitbart London Editor in Chief Raheem Kassam.

Pointing to Prince Harry’s politicised interview with Barack Obama on the BBC’s flagship news programme Wednesday, in which the former president launched a thinly-veiled attack on President Donald Trump, Harris-Quinney blasted the royal for “clearly politicising” his role in the family.

“More significant than this radio interview I think, is his insistence on inviting Obama to his upcoming wedding, which will be a state event, and making a point to snub Donald Trump.”

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The Bow Group boss said it was “madness” for members of the Royal family to turn their backs on conservatives — who are key to their support — in favour of cosying up to liberals who have no respect for the institution.

“What these people don’t seem to realise is their support lies among conservatives, and they might enjoy dinner parties a bit more in taking left-wing positions, but ultimately they will see their own dissolution,” he told Kassam.

“It is a kind of madness that they’re engaged in, which is this idea that they will feed the progressive agenda in the hope that it will eat them last,” he continued, pointing out that liberal-courting royals like Prince Harry are spurning a president who “loves Britain [and] loves the Royal family”.

“But many members of the Royal family don’t want to know about Donald Trump,” he said. “They want to know about Barack Obama, a guy who hates the British Empire, hates British history, hates the monarchy.”

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“The Royal family needs to make a decision on whether they want to survive”, said Harris-Quinney, urging it to start courting conservatives and “shun away this Huffington Post and Barack Obama nonsense” or else the family will lose its primary base of support.

“Our support is conditional,” the think tank chief told Kassam, contending that conservatives have no intention of backing “several generations of virtue-signallers living off the public purse and not contributing anything to the maintenance of British society”.