A Labour pressure group backed by Andy Burnham has demanded the "total overhaul of personnel" in Downing Street amid the fallout from the Peter Mandelson scandal.
Mainstream’s interim council called for a "clean break" after the "betrayal" of the peer's appointment to "one of the most powerful diplomatic posts on the planet" despite his friendship with paedophile financier Jeffrey Epstein being public knowledge.
The centre-left grouping, which is backed by the Greater Manchester mayor - long seen as a potential leadership rival to Sir Keir Starmer - said its members did not want to watch the party "succumb to the same old sickness" of "elite privilege, spin and toxic factionalism".
It comes as the Prime Minister apologised to the victims of Epstein on Thursday, saying he is "sorry for having believed Mandelson's lies” and appointing him Britain’s ambassador to Washington.
Sir Keir insisted that "none of us knew the depth of the darkness" of Lord Mandelson's relationship with the sex offender.
Speaking at an event in East Sussex, Sir Keir addressed the scandal as he fights to save his premiership.
"It has been publicly known for some time that Mandelson knew Epstein, but none of us knew the depth of the darkness of that relationship," the PM said.
Mainstream’s interim council, which includes MP Alex Sobel, said the disgraced former minister’s appointment as US ambassador was "the direct result of a corrosive political culture that must be torn out by its roots".
They added: "A failure of this magnitude does not happen by accident. It requires a system that elevates factional loyalty over integrity, that values connections over character and that treats rigorous vetting as an inconvenience.
"Everyone who participated in this process - from those who championed the appointment, to those who turned a blind eye, to those who silenced doubts in the name of political convenience - must be held to account."
Criticising a "politics of deference and backroom patronage", Mainstream called for an end to "a culture that fears internal challenge".
"While this is a systemic failure, those who designed and operated the system cannot evade consequence, they said.
“True accountability means a total overhaul of personnel, of process and of the rotten priorities that brought us here. We will not settle for less."
Tory leader Kemi Badenoch said the Prime Minister and his right-hand man Morgan McSweeney should both be in the firing line to lose their job over the Mandelson affair.
She told a press conference in Westminster: "I think that if it is not Sir Keir Starmer then it should be Morgan McSweeney - both of them have a lot to answer for and both of them are hiding."
Asked if it would make any difference if the Prime Minister sacks Mr McSweeney, she said: "I think that what has happened is so serious that someone should go for it, someone needs to take responsibility - that's why we asked for the files to be released.
"It is not so we can read lots of juicy gossip about Mandelson - it's so we know who took that decision and when because it has embarrassed our country on the international stage, it made us weaker from national security perspective and it left us exposed.
“Someone needs to take responsibility. All we are hearing from Sir Keir Starmer is 'Peter Mandelson lied to me'.
“They are trying to put it all on Peter Mandelson but it's not all on Peter Mandelson - it is also on Downing Street.
"I think that if it is not Sir Keir Starmer then it should be Morgan McSweeney - both of them have a lot to answer for and both of them are hiding."
