Former deputy Labour leader Baroness Harman has branded Sir Keir Starmer’s response to the Lord Mandelson saga as “weak, naive and gullible”.

She warned the Prime Minister risks being toppled by the fiasco “unless he takes action”.

Speaking to Sky’s Electoral Dysfunction podcast, Baroness Harman said: “I think it is so serious for Keir Starmer. I don’t think it’s inevitable that it will bring him down.

“But it will bring him down – unless he takes the action, which is really necessary for him to take, and that’s this: firstly, he’s got to stop blaming Mandelson and saying, ‘he lied to me’. Because actually, he should never have been considering him in the first place.

“To say ‘he lied to me’ makes it look weak and naive and gullible. So it’s just completely the wrong thing.

“He should be reflecting on why he made that appointment, not be angry at the evilness of Peter Mandelson.

“He should also be thinking about a real reset in No 10, because what you need from your team in No 10 is people who share your values and your principles and who will help you be the best prime minister you can be, according to your true self.

“Clearly, that is not what happened because the Keir Starmer, who was DPP [director of public prosecutions], would never have appointed somebody like Peter Mandelson to represent the country.”

The Prime Minister has attempted to defend himself by claiming Lord Mandelson lied to him and he was not aware of the full extent of his relationship with Epstein.

Sir Keir apologised to the victims of Epstein, saying he is “sorry for having believed Mandelson’s lies and appointed him” British ambassador to Washington.

The Prime Minister insisted that “none of us knew the depth of the darkness” of Lord Mandelson’s relationship with the convicted sex offender when he was picked for the role.