Shailesh Vara appointed as new Northern Ireland secretary

Mr Johnson is set to remain as prime minister until a successor is in place, expected to be by the time of the Conservative Party conference in October.

This is despite critics suggesting he should not be allowed to stay in office until the autumn.

Mr Lewis announced his resignation early on Thursday, tweeting a copy of his resignation letter in which he told Mr Johnson that he had “given you, and those around you, the benefit of the doubt”.

“We are, however, now past the point of no return.

“I cannot sacrifice my personal integrity to defend things as they stand now. It is clear that our Party, parliamentary colleagues, volunteers and the whole country, deserve better,” he said.

NIO minister Conor Burns indicated he will remain in post, tweeting that he will lead for the government at a meeting of the British-Irish Council.

“It is vital at this time that the job @NIOgov continues to be done.

“I am committed to continuing to serve the wonderful people of Northern Ireland to the best of my ability at this tough time,” he said.

Mr Lewis was blasted by Sinn Féin Stormont leader Michelle O’Neill as having “shamefully placated the DUP”.

She claimed he “abandoned any pretence of acting with the ‘rigorous impartiality’ required of him under the Good Friday Agreement”.

“He has shamefully placated the DUP by giving them political cover in denying the electorate the democratic representation they are entitled to,” she said.

The Stormont Assembly remains collapsed amid a row over the Northern Ireland Protocol.

The DUP is refusing to nominate ministers to the executive or a speaker to allow the Assembly to function until the UK government takes action on the post-Brexit arrangements.

Meanwhile SDLP leader Colum Eastwood said Mr Johnson has “debased the office he holds”.

“He has fundamentally and indelibly damaged public confidence in politics and public life and his death grip on power has prolonged a period of government that will be characterised by law-breaking, scandal and sleaze.

“He should now leave government immediately,” he said Ms O’Neill was also critical of Mr Lewis over his proposed bill for dealing with Northern Ireland’s troubled past.

The Northern Ireland Troubles (Legacy and Reconciliation) Bill offers an effective amnesty for Troubles crimes for those who co-operate with an information body.

She added: “He has undermined the Good Friday Agreement and political stability, and his actions gave us a daily reminder why those with no mandate or votes here will only ever act in their own political interests, and not ours.

“The political stability of the North cannot be a hostage to the Tory-in fighting, Westminster chaos and continued DUP disruption.” Alliance MP Stephen Farry described a “completely crazy situation” and said Mr Johnson was a “narcissistic self-entitled fool”.

“The fact it even got to this point is damning in itself,” he said, and also questioned the DUP’s silence on Mr Johnson.

Prominent victims campaigner Raymond McCord welcomed the resignation of Mr Lewis.

Mr McCord said: “He (Mr Lewis) has betrayed the victims of the Troubles with the Legacy Bill that gives an amnesty to murderers.

“Brandon Lewis decided to reward the murderers with amnesties for the murders they committed, and punish the victims and their families by ensuring all routes to justice and even civil cases are closed down.

“He insulted all victims by claiming it would help us.

“He certainly will not be missed by victims.”