Keir Starmer has threatened to call a vote of no confidence in the government if Boris Johnson is allowed to “cling on” in No.10.
If successful it could lead to a snap general election. It would need some Conservative MPs to vote with the opposition parties to pass.
The prime minister has announced he will resign, after suffering waves of resignations from his government.
But he has suggested he could stay on as PM in a caretaker capacity until October when the Conservative Party has elected a new leader.
Several Tory MPs have already reacted angrily to the idea. Simon Hoare, the chairman of the Commons Northern Ireland committee, said it was “beyond credulity that Mr Johnson can stay in office even pro tem”.
Nick Gibb, a former schools minister, said: “As well as resigning as party leader the PM must resign his office.”
Speaking on Thursday morning, Starmer said: “He needs to go completely. None of this nonsense about clinging on for a few months.
“He’s inflicted lies, fraud and chaos in the country. We’re stuck with a government which isn’t functioning in the middle of a cost of living crisis.
“And all of those that have been propping him up should be utterly ashamed of themselves.”
The Labour leader added: “If they don’t get rid of him then Labour will step up and bring a vote of no confidence.
“He needs to go. He can’t cling on,” he added. “They cannot inflict him on the country for the next few months.”
Many Tory MPs would like Johnson to leave soon, with Dominic Raab, the deputy prime minister, serving as caretaker PM.