BORIS Johnson’s bunker is unmistakably collapsing, Dominic Cummings has said following the resignation of a key No 10 aide.

Munira Mirza, one of Johnson’s most trusted advisers, handed in her resignation after the Prime Minister used Jimmy Savile to try and smear the leader of the Labour party, Keir Starmer.

In her resignation letter, the now former head of the No 10 policy unit said it had been “an inappropriate and partisan reference to a horrendous case of child sex abuse”.

She went on: “You tried to clarify your position today but, despite my urging, you did not apologise for the misleading impression you gave.

READ MORE: Keir Starmer, Jimmy Savile, and the Tories' 'move towards disinformation'

“You are a better man than many of your detractors will ever understand which is why it is so desperately sad that you let yourself down by making a scurrilous accusation against the Leader of the Opposition.”

The resignation of one of his most loyal allies, who has worked with him for more than a decade, further weakens the Prime Minister as he battles to remain leader.

Johnson once praised Mirza as a “brilliant thinker” and listed her as one of the five women who had influenced and inspired him the most.

Her resignation has been labelled a huge loss for Johnson’s No 10, with Cummings predicting it will be the start of a “mad scramble” away from the Prime Minister.

He wrote on Twitter: “Moral courage from Munira who has done her best to make progress with a professional team throughout the horror since 11/20 [November 2020, when Cummings quit Downing Street].

“It's also an unmistakable signal the bunker is collapsing and *this PM is finished*. Flicker of moral courage from Cabinet and Cabinet Office asap please.

“Pretty soon there will be a mad scramble and ministers will be kicking themselves hitting their heads saying ‘WHY didnt i move faster arghhh’.

“Now’s your moment, find a flicker of moral courage and ‘push what is falling’.”

Nikki da Costa, the former director of legislative affairs at No 10 Downing Street, commented on Twitter: “Munira was the very best of No 10 - this is a huge loss. Know her team will feel this acutely and valued her leadership, encouragement, steadiness, fairness and values. Brilliant at interrogating the arguments she made us all think deeper and want to do better.”

The SNP's deputy leader at Westminster, Kirsten Oswald, said Boris Johnson's position was "completely untenable".

The National:

She went on: "He has broken his own Covid rules, misled parliament, and now one of his most trusted advisers is jumping ship out of disgust for his lies.

"If Mr Johnson won't go willingly, then Tory MPs must force him from office. The longer he stays in post, the more damage he will do to any remaining public trust in the Westminster government.

"Luckily for People in Scotland we have an alternative to the constant crisis of Westminster control. Scotland can become an independent country and escape the broken Westminster system for good."