87 Labour MPs have now called for Starmer's resignation, to which Starmer has replied, "When you take it from my cold, dead hands."
No one wants to be the first to openly challenge for the head of the party and PM, because the person who moves first rarely wins. The two major candidates seem to be Wes Streeting and Manchester mayor Andy Burnham (think AOC). Problem is Burnham is not a member of Parliament so not eligible. He allegedly has already lined up a seat, he just needs that person to resign and win the by-election. That likely means making a deal with the Green Party so they don't run a candidate of their own and stop him. Their platforms are heavily aligned, so it shouldn't be that difficult to do.
My guess is that Streeting realizes if he hesitates his chance to be PM will disappear and will be forced to make his move before Burnham can be seated. Then it's a choice between going for Streeting now or waiting until end of summer when Burnham will likely be ready. Hopefully the party chooses to wait. Burnham can offer a clean slate, follow through on the progressive campaign promises Starmer made and has broken, and a Labour-Green coalition (with the SNP and Plaids) can regain the support of the people and prevent the Nazis from taking over at the next general lection in 2028 or 2029. If Labour go with Streeting it's almost certain the Fascists will win in 2029.