THE “perverse” rule that requires MPs to swear allegiance to the King and all of his heirs or face losing their seat in parliament should be changed, campaigners say.

It comes after Labour MP Clive Lewis revealed that he had been forced to retake the oath after initially omitting to swear allegiance to all of the monarch’s “heirs and successors”.

Lewis had only sworn the oath under protest the first time around, and has now called for the legal ceremony to be changed.

He wrote on social media: “After omitting to swear allegiance to King Charles's ‘heirs and successors’ last week, I've had to take the oath again in order to sit in the House of Commons.

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“The majority of the public are committed to democracy, and so I hope one day MPs can swear an oath based on those values.”

Lewis further shared a letter of warning he had received, adding: “If I had not re-sworn the oath, then based on a law from 1866, I could be fined, subjected to legal action, and my seat ‘shall be vacated in the same manner as if [I] were dead’.

“This should change, so MPs have the choice to swear allegiance to our constituents and democracy.”

It understood that the Labour MP was the first ever called on the retake the oath.

Campaign group Republic seconded Lewis’s calls for a renewed swearing in system, calling the current one “outdated” and highlighting that a pledge of allegiance to royal heirs included Prince Andrew.

Republic chief executive Graham Smith said: "Millions of people in the UK support the abolition of the monarchy. Whether they become MPs, police officers or join the armed services, their allegiance will always be to their country and fellow citizens, not an unelected head of state.

"The oath is particularly perverse in parliament, where the right to take your seat should come only from the votes cast on election day. To be told you must swear allegiance to a monarch is outdated nonsense that flies in the face of freedom of expression."

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He added: "The vast majority of people in the UK support democracy and free speech. The slightly hysterical reaction to Clive's oath taking last week was confined to a small minority on the right.

"Clearly it's time to introduce a choice, where MPs can choose to swear their allegiance either to the king or to their country and constituents. This should not be a controversial notion in a democratic society."

In all, it took Westminster three days to swear in the 643 MPs who will take their seats.

Former Labour leader Jeremy Corbyn could be heard to call the parliamentary tradition “a load of nonsense” while waiting to be sworn in.

Any changes to the oath would require legislation from the UK Government.