Jo Johnson, the younger brother of British Prime Minister Boris Johnson, on Thursday resigned his post as a minister and stepped down as a member of Parliament.

In a tweet announcing his resignation, Johnson said he was "torn between family loyalty and the national interest."

Jo Johnson is a staunch supporter of remaining in the European Union and backs holding a second Brexit referendum.

His resignation came with discontent growing in the Conservative Party after Boris Johnson expelled more than 20 Conservative lawmakers who voted to delay Brexit.

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Jo Johnson, the younger brother of British Prime Minister Boris Johnson, has dramatically resigned as a Conservative Party minister and member of Parliament, saying in a tweet Thursday that he is "torn between family loyalty and the national interest."

Johnson, unlike his brother, supports remaining in the European Union and has called repeatedly for a second Brexit referendum and was also reportedly unhappy about his elder brother's decision to expel 21 Conservative lawmakers from the party.

He was the MP for the Orpington constituency on the outskirts of London and was also the minister of state for universities, science, research and innovation.

Speaking after his resignation Jo Johnson suggested that his brother should move back to the centre ground of British politics.

"What is so clearly in the national interest is everything the Government is doing in its strong, One Nation domestic policy agenda: more police on the streets, more doctors and nurses in our hospitals, a welcoming face to scientists and international students," he told the Sun newspaper.

"That's exactly what a Conservative prime minister should be doing and what Boris does so well."

A representative of Boris Johnson said the prime minister "would like to thank Jo Johnson for his service," adding he had been "a brilliant, talented minister and a fantastic MP."

They added that "The PM, as both a politician and brother, understands this will not have been an easy matter for Jo."

The development was received with derision by the government's opponents.

"Boris Johnson poses such a threat that even his own brother doesn't trust him," Labour's shadow education secretary, Angela Rayner, said in a statement.



The prime minister has previously dismissed suggestions that he would fall out with his brother while in office.

Asked by The Telegraph in 2013 whether his brother would "shaft" him in the same way the opposition Labour MP Ed Miliband did when he successfully challenged his brother David for the leadership of their party, Boris Johnson replied: "Absolutely not. We don't do things that way, that's a very left-wing thing."

He added: "Only a socialist could regard familial ties as being so trivial as to shaft his own brother."

Jo Johnson's resignation comes after his brother was thwarted in a bid to call an early election in October, just weeks before the UK is set to leave the European Union.

The UK Parliament has yet to approve a Brexit deal, and unless it is able to do so before October 31, the UK will drop out of the EU with no deal.

Boris Johnson. Getty

Discontent in the Conservative Party has grown in recent days after Boris Johnson decided to expel 21 senior Conservative lawmakers from the party after they backed a bill that would see Brexit delayed until 2020.

Read more: What happens now MPs have voted to delay Brexit until 2020?

The ousted MPs, who included two former chancellors and Winston Churchill's grandson, are popular figures in the party, and Boris Johnson has reportedly been challenged by leading members of his cabinet to repeal their expulsion.

The younger Johnson had previously resigned from his position as a minister in the cabinet of his brother's predecessor, Theresa May, where he served as a transport minister.

He had also opposed May's approach to Brexit, saying at the time that the UK was "barreling towards an incoherent Brexit."