But Mr Johnson told his new Cabinet he would not make any major policy changes, leading to questions about how he could handle the policy challenges of the coming months.
A Downing Street readout of the meeting said of the Prime Minister: “He made clear the Government would not seek to implement new policies or make major changes of direction, rather it would focus on delivering the agenda on which the Government was elected. He said major fiscal decisions should be left for the next prime minister.”
Sir Robert Buckland, who returned to the Cabinet on Thursday as Welsh Secretary, said: “This Prime Minister no longer has the political authority to do new things,” a sign of how constrained Mr Johnson will be in office.
In the coming months strikes from teachers, postal workers, doctors and rail workers all loom, in part over a stand-off on pay – although decisions are yet to be taken by trade unions.
The economy is faltering, with inflation soaring and recession forecast as early as the end of the year. A stand-off with Brussels over Northern Ireland’s post-Brexit trade terms remains.
Supporters of Mr Johnson’s position countered by noting that both Theresa May and David Cameron remained in No 10 while a race to succeed them took place.
There is also no official position of “acting prime minister” recognised in Britain’s constitutional history, making it unclear if an MP stepped into such a role how it would work.
George Freeman, who quit as science minister on Thursday morning, said: “Unfortunately, it’s very difficult to see how Boris Johnson, given the character that he is, is going to be able to govern for three months in quiet humility and contrition. That certainly wasn’t the tone of his speech.
“My real worry is the instability will fuel a febrile moment of midsummer madness, where we choose the wrong person in a hurry because of the instability. We can’t afford to do that.”
Andrea Leadsom, the former business secretary who has stood twice for the Tory leadership, said: “I absolutely do not think that it is acceptable that we have a long, drawn-out leadership campaign.
“It is my opinion that Boris would be better to go now and salvage what is a good track record in some really key major events.”
Simon Hoare, a backbench MP, said on Twitter: