Chancellor Philip Hammond has sent a thinly-veiled warning to Boris Johnson amid speculation that the Foreign Secretary is trying to destabilise Theresa May, declaring "nobody is unsackable".
Mr Hammond affirmed his "100% support" for the Prime Minister and denied reports that he had sent a 4am text to Mr Johnson on the night of the general election offering him his support for the leadership.
The Conservative conference in Manchester has been dominated by discussion of Mr Johnson's leadership ambitions, after he set out his own personal red lines for Brexit negotiations and issued a call for higher public sector pay rises.
Former education secretary Nicky Morgan said on Sunday night that Mr Johnson "had to go" unless he could show his loyalty to the Government, while the British Chambers of Commerce warned that public disagreements between Government ministers were damaging business confidence.
Mr Hammond acknowledged that uncertainty over EU withdrawal negotiations were causing "a pause in business investment" which was harming the UK economy, and said it was the duty of all Cabinet ministers to "pull their weight" in support of the Prime Minister.
Asked whether Mr Johnson should be sacked, the Chancellor told ITV's Good Morning Britain: "We all serve at the Prime Minister's pleasure and we all owe the Prime Minister our allegiance and our loyalty within the Cabinet.
"I have always operated on the principle that it is probably best to believe that nobody is unsackable. Everybody has got to pull their weight within the Government."
Mr Hammond's intervention came as he tried to keep attention on the domestic agenda, with the announcement of £400 million for transport links in the North of England.
Some £300 million will be used to ensure cities like Liverpool, Manchester, Sheffield, Leeds, York and Leicester can be linked up with the HS2 high-speed rail route between London and the North.
And a further £100 million will go into local road schemes to cut congestion and unlock new sites for homes and businesses in the North.
Mr Johnson expressed surprise that his article stating the Brexit transition period should last "not a second more" than two years had overshadowed the first day of the Manchester conference, squeezing out Mrs May's attempts to make a pitch to younger voters.
The Foreign Secretary told the Daily Telegraph: "I think, actually, if you studied what I said, it was basically Government policy. I think it's extraordinary that so much fuss has been made about repeating Government policy, but there you go."
Mr Hammond flatly denied reports that he had offered Mr Johnson his support as leader in an early-morning text as the disastrous results of the June 8 election became clear.