On the steps of Downing Street just two weeks ago, Rishi Sunak sought to draw a line under both of his recent predecessors’ chaotic administrations, vowing that his would be one of “integrity, professionalism and accountability at every level”. But on Tuesday the prime minister’s promises – already shaken by his appointment of Suella Braverman as home secretary six days after she was sacked by Liz Truss, and his failure to fill the long-vacant ethics adviser role – took yet another battering as Gavin Williamson, the twice-sacked Cabinet Office minister, left the government under a dark cloud. Williamson was spotted going in and out of No 10 several times on Tuesday, as the fight to save him went down to the wire. One insider said he was even seen smiling as he emerged into the adjoining Cabinet Office, giving the impression that it was business as usual. The Guardian has learned that despite reports that he had offered to quit earlier that morning, attempts remained under way to avoid bowing to the inevitable amid growing pressure from Tory MPs. Initially, the government was preparing to issue a statement trying to draw a line under the allegations already made, and those expected to surface. It would have tried to placate critics by saying the Cabinet Office minister would be attending anti-bullying training but remain in post. However, the robust defence of his position was never issued – and later in the afternoon one government source put the chances of his dismissal at 80%. As the senior civil servant whom Williamson allegedly told to “slit your throat” said they would make an official complaint, and after his former deputy chief whip, Anne Milton, criticised his “unethical and immoral behaviour”, No 10 insiders were getting jittery. Senior Tory MPs began raising concerns with No 10 – by phone and in person – about Sunak’s decision to stand by Williamson. “This stuff matters – we should be setting the standard for acceptable and civil behaviour in public life,” one muttered. Another said that given the row over Braverman, Sunak had shown that concerns about his lack of political nous were “not a one-off”. One angry former minister said: “Sunak just needs to fire him. Every minute he leaves it more stuff comes out and it’s more damaging. It’s madness. Gavin just needs to get kicked out. He shouldn’t even be allowed to resign.” Then at about 6pm, Williamson headed into No 10 for the final time. A Downing Street source tried to suggest the visit was routine for a minister who works next door in the Cabinet Office, but the Guardian understands the showdown was to discuss the media coverage of his conduct and whether the situation was sustainable. No 10 has admitted that Williamson requested the face-to-face meeting with the prime minister – and denied that Sunak had originally refused to accept his resignation. “It was the right thing to do to resign,” said one insider, but it was still unclear whether Sunak would have sacked his close political ally if he hadn’t.