Former Speaker of the House of Commons and Tory MP John Bercow says he has changed allegiances to join Labour.

He told the Observer the Conservatives under Boris Johnson were “reactionary, populist, nationalistic and sometimes even xenophobic”.

The government “needs to be replaced”, said Mr Bercow, who made controversial procedural decisions over the Brexit process during his time as Speaker.

A senior government source said: “This will surprise nobody.”

It “shows Labour is still the party of Remain”, the source added.

Mr Bercow stood down as Speaker and MP in November 2019 after a decade in the job. He had been a Tory MP for 12 years before taking the role.

Because the Speaker has to be politically impartial, he had to resign from the party when he was elected Speaker in 2009.

During his time as Speaker, he gave unprecedented and controversial powers to backbenchers during debates over Brexit.

He also had several run-ins with the Conservative Party, including in 2015 when he survived an attempt by Conservative whips to oust him just before the election.

In an interview with the Observer, Mr Bercow said: “I am motivated by support for equality, social justice and internationalism. That is the Labour brand.

“The conclusion I have reached is that this government needs to be replaced. The reality is that the Labour Party is the only vehicle that can achieve that objective. There is no other credible option.”

He told the newspaper he joined Labour a few weeks ago. The Labour leader’s office declined to comment.

Speaking to Sky News, he said he hadn’t felt “the slightest desire” to rejoin the Conservative Party when he stepped down as Speaker.

Although he hit out at the prime minister as a “lousy governor” with “contempt” for Parliament, he said his decision was “not personal against Boris Johnson”.

His political beliefs, he added, had evolved “over a long period”.

On his retirement as Speaker, Downing Street declined to put forward Mr Bercow’s name for consideration for a peerage by the House of Lords Appointments Commission. Instead, the Labour opposition nominated him.

In February 2020, he told the BBC there was a “conspiracy” to keep him out of the House of Lords.

He said it was “blindingly obvious” that there was a “concerted campaign” to prevent him from being given a peerage, a position conventionally offered to former Speakers.

Asked if there is the possibility of being recommended for a peerage by Labour leader Sir Keir Starmer, Mr Bercow told the Observer: “There has been no such discussion and I have asked for no such thing.

“This isn’t about revenge. That is not what motivates me.”

John McDonnell, Labour’s shadow chancellor under Jeremy Corbyn, said Mr Bercow had been “scrupulously fair” in his treatment of MPs, including the former Labour leader.

“He won our respect, especially for his fight to protect the rights of Parliament,” he said. “I wholeheartedly welcome him into the Labour Party.”

Tory pensions minister Guy Opperman said: “Labour are welcome to Bercow.”

In response to Mr Bercow’s interview, a senior government source said: “The prime minister has an ambitious agenda to build back better from the pandemic and level up across the UK.”

The source said the impact of the pandemic had “forced us to take tough but necessary decisions on how we spend taxpayers’ money”, including on international aid.