Health Secretary Wes Streeting has resigned from the cabinet and is expected to trigger a leadership contest.
Streeting met with Starmer in Downing Street on Wednesday morning, leaving No.10 after just 16 minutes. The Times reported that Streeting had told the prime minister that he was preparing to challenge him for the leadership.
It was later widely reported that Streeting was expected to resign as soon as Thursday morning and fire the gun on a leadership election.
In his resignation letter to Starmer on Thursday, Streeting said there "many good reasons" to remain in post, but added: "As you know from our conversation earlier this week, having lost confidence in your leadership, I have concluded that it would be dishonourable and unprincipled to do so."
Streeting said that, under Starmer's leadership, there is a "vacuum" instead of "vision", and "drift" instead of "direction".
"Leaders take responsibility, but too often that has meant other people falling on their swords," he added.
As of Wednesday, four ministers had resigned from government, including health minister Zubir Ahmed, who is a close ally of Streeting.
On Wednesday, CSW's sister publicationPoliticsHome reported that junior minister Josh MacAlister, Labour MP for Whitehaven and Workington, had told the Prime Minister to set out a timetable for his departure.
At the time of writing, more than 90 Labour MPs have publicly called for Starmer to resign.
On Tuesday,PoliticsHome reported that Darren Jones, chief secretary to the Prime Minister, had sparked suspicion among colleagues that he was seeking support for his own leadership bid.
Energy secretary Ed Miliband is also seen as a potential contender for the leadership. Miliband's allies told PoliticsHome on Wednesday that he would have the numbers to stand in a leadership contest if Manchester mayor Andy Burnham cannot get a seat in time.
Angela Rayner revealed in an interview with The Guardian on Thursday morning that she had been cleared by HMRC of deliberate wrongdoing or carelessness over her tax affairs. It means that Rayner could put her name forward in a bid for the leadership.
This article was written by Matila Martin, a reporter at CSW's sister publication PoliticsHome, where a version of this story first appeared