Bercow, who clashed with Prime Ministers Boris Johnson and Theresa May over their approach to Brexit and treatment of parliament, told the Observer newspaper that he now believed the Conservative Party was "reactionary, populist, nationalistic and sometimes even xenophobic".

As speaker from 2009 to 2019, Bercow brought attention to the normally low-key role with his distinctive calls for order and his readiness to aid lawmakers' challenges to May's and Johnson's attempts at passing Brexit legislation.

Many Conservatives and Brexit supporters felt he lacked the political neutrality required by the position of speaker.

Bercow told the Observer he now wanted to help the Labour Party oust Johnson from office.

"I am motivated by support for equality, social justice and internationalism. That is the Labour brand," he said. "The conclusion I have reached is that this government needs to be replaced."

Bercow entered parliament as a Conservative in 1997, and according to parliamentary convention his electoral district was not contested by other main parties after he became speaker.

During his time as speaker he faced several accusations of bullying parliamentary staff, all of which he denied.