Tory leadership contender Penny Mordaunt said Boris Johnson had put “country before party” by deciding against running in the race to replace Liz Truss.
Mr Johnson confirmed on Sunday evening that he had pulled out of the running to return to No 10.
The former prime minister said he had “reached out” to leadership rivals Rishi Sunak and Ms Mordaunt to see if they could work together in the national interest, but it had not proved possible.
In a post on Twitter reacting to Mr Johnson’s decision, Ms Mordaunt said “In taking this difficult decision last night Boris Johnson has put country before party, and party before self.
Penny Mordaunt
Aaron Chown
Boris Johnson
Aaron Chown
“He worked to secure the mandate and the majority we now enjoy.
“We should put it to good use, and I know he will work with us to do so.”
In a statement on Sunday, Mr Johnson insisted he had secured the 100 nominations needed to get onto the ballot paper – and that if he stood there was a “very good chance” he would be back in Downing Street by the end of the week.
He went on: “But in the course of the last days I have sadly come to the conclusion that this would simply not be the right thing to do.
“You can’t govern effectively unless you have a united party in Parliament.
“And though I have reached out to both Rishi and Penny – because I hoped that we could come together in the national interest – we have sadly not been able to work out a way of doing this.
“Therefore I am afraid the best thing is that I do not allow my nomination to go forward and commit my support to whoever succeeds.”
Mr Johnson’s withdrawal leaves the election to replace Liz Truss as potentially a straight fight between Mr Sunak and Ms Mordaunt.
It could all be over a little after 2pm on Monday if Ms Mordaunt – who so far has fewer than 30 public declarations of support from MPs fails – to enough nominations to go forward.
Her supporters will be hoping that the departure of Mr Johnson will open up the contest, enabling her to make it onto the ballot paper.
If she does, MPs will hold an “indicative vote” to show who they support and there will then be an online poll of activists to decide the contest – unless one or other of the candidates stand down