Gloucester MP Alex McIntyre says he has signed a letter calling for a change of leadership within the Labour Party and Government.
In a statement posted on social media, Mr McIntyre said he remained proud of many changes made by the Government but believed “too many mistakes” had also been made.
He criticised the appointment of Peter Mandelson, saying the decision was “at odds” with what public life should represent.
Mr McIntyre said conversations with constituents and recent election results had convinced him that the Prime Minister no longer had sufficient public backing to deliver change.
He added that Gloucester residents deserved leadership capable of meeting the country’s challenges and said he no longer believed the Prime Minister was the right person to lead that effort.
Despite the criticism, he said he still believed a Labour government could deliver a better future if it “changed course” and found new leadership.
Forest of Dean MP Matt Bishop and Stroud MP Simon Opher have also called for the Prime Minister to resign.