Andrew Boff, one of London’s longest-serving Conservative politicians, has quit the party after 53 years. Mr Boff, 68, announced his resignation on Tuesday.

He said he had been blocked from seeking the Conservative nomination for mayor of London because he supports the European Convention on Human Rights (ECHR). He will keep his seat on the London Assembly, which he first won in 2008, and will now sit as an independent London-wide member.

London’s voting system differs from general elections, so Mr Boff was elected from the Conservative Party’s list rather than directly for a seat. The role pays ยฃ66,290 a year.

Mr Boff, who joined the party in 1973, called the decision to block him “extraordinary and profoundly disappointing”. In a statement, he said the ECHR was not a “Left-wing project” but a “safeguard against arbitrary government”.

He pointed out that British Conservatives, including Winston Churchill, helped create it after World War 2. He added: “I have not abandoned my Conservative principles. I believe the party has abandoned some of its own.”

The party’s position is that it will leave the ECHR, a policy announced by leader Kemi Badenoch. Last year, she told GB News that anyone who did not agree “should not and cannot stand as a Conservative candidate”.

Mr Boff has long backed the Convention and has sought the mayoral nomination before. He tried to do so again this year before being stopped by party HQ.

He has previously made headlines for public protests. He was escorted out of the main hall during a speech by Suella Braverman, then a Conservative, after heckling her over her position on transgender issues โ€“ wearing a T-shirt reading “Trans Rights Are Human Rights”.

He was also seen handing out leaflets backing the ECHR at Conservative Party Conference earlier this month, despite officials warning him not to.

Susan Hall, leader of the London Conservatives, said: “We deeply regret to hear that Andrew Boff AM has decided to leave the Conservatives”. She said the party stands by its commitment to leaving the ECHR.

Fellow list member Emma Best AM has called on him to give up his Assembly seat “for integrityโ€™s sake”.

In an online post, she said: “Andrewโ€™s a list member. That means Londoners didnโ€™t vote for us, they literally voted โ€˜Conservativeโ€™. Let the next Conservative on the list step up.”

A senior London Conservative told the Daily Express that Mr Boff long saw himself as “a martyr for every cause which sets him apart from mainstream opinion”.

They said he “threw his toys out the pram when he didnโ€™t get short-listed to be our mayoral candidate”. But they added that he “didnโ€™t have a problem remaining in the Conservative Party for over a year after Kemi first announced our position on the ECHR.”

Another London Conservative said they had been asked to “keep an eye on him” at Tory conference in case he staged a protest.