Last week, Labour saw another humiliating defeat after losing the Hartlepool by-election to the Conservatives by a majority of almost 7,000. The area was previously seen as a Labour stronghold.

Following their defeat, Sir Keir shuffled his party which saw deputy leader Angela Rayner removed from her role as party chairwoman.

Anneliese Dodds was also sacked as Shadow Chancellor, along with other personnel changes.

Now, amid an ongoing civil war within the party, Ms Harris stepped down as the Labour leader’s parliamentary private secretary in a huge blow to the Opposition leader.

It is believed supporters of Ms Rayner demanded Ms Harris’s scalp after blaming her for dodgy briefings.

The Guardian reported the accusation is thought to have been made by a veteran MP and that it was said to be part of a “briefing war”.

Ms Harris did not comment to the Guardian.

Announcing her departure from the role, Ms Harris said it had been an honour to serve Sir Keir.

In a statement, the MP for Swansea East said: “It has been the proudest moment of my career to co-chair the campaign that saw Keir Starmer elected as Labour leader, and to serve as his PPS for the past year.

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One ally told The Times: “She’s come out of this so much more powerful after a year of being held back.

“On Friday Keir couldn’t answer a simple question about what Labour’s vision is, what our offer is and how we will win back the voters in our heartland seats.

“Angela can answer that question.”

Labour lost eight votes across England in the elections last week while the Conservatives saw an increase of 13 new seats.

Sir Keir said he takes full responsibility for Labour’s defeat and said it is “entirely” on him.

He told the Shadow Cabinet: “To be clear, I take responsibility. Nobody else.

“I lead the Labour Party and it is entirely on me.”

Sir Keir saw his popularity plummet following the disastrous election defeat.

A YouGov poll asked how well Labour is doing, just 17 percent had a favourable view of the leader of the Opposition.

In a further blow to the Labour leader, 65 percent of those asked had a poor view of Sir Keir’s performance.

In comparison with April, the poor approval of Sir Keir has increased by 15 percent while those who thought he has done well, has dropped by nine percent.

As seen by YouGov’s approval tracker, Sir Keir’s disapproval rating has risen sharply in the last two months.