Lisa Nandy has broken ranks to become the first Cabinet minister to join Andy Burnham on the campaign trail in Makerfield.

The Culture Secretary accompanied the Mayor of Greater Manchester as he canvassed voters in the Wigan constituency, where he is hoping to win a by-election on June 18.

The sight of one of Sir Keir Starmer’s senior ministers campaigning with a likely leadership challenger will be seen as an embarrassment for the Prime Minister. Mr Burnham failed to say on Saturday that he had confidence in Sir Keir.

Sharing a photograph of herself with Mr Burnham and other Labour activists, Ms Nandy said on X: “Good to be out on the doors in Winstanley today and lovely to see some good friends come over to help.

“Life has been too tough for people in this borough for too long, but we are determined to turn this around.”

Ms Nandy failed to explicitly back Sir Keir after last week’s historic local election defeat and acknowledged that many Labour campaigners were “hurting”.

A day after the election, she said: “As the Prime Minister says, it is clear the public are impatient for change and we must rise to meet this moment and deliver change on the scale that people need and have asked for.”

Following Sir Keir’s reset speech on Monday, Ms Nandy said that the speech alone was not enough and went on to suggest the Cabinet was not fully united in its support for the Prime Minister.

She has also not shied away from criticising Sir Keir in the past, hitting out at a “boys’ club” culture in Downing Street after she and other female frontbenchers were the subjects of hostile briefings.

In February, Ms Nandy gave a memorable interview in which she attacked the Prime Minister’s handling of the Mandelson scandal by saying: “You call it a s---show, I say it’s unforgivable.”

Mr Burnham was blocked by Sir Keir and his allies from standing in Gorton and Denton in February but will be allowed to stand in Makerfield if approved by the local Labour party.

He is currently ineligible to challenge for the leadership because he is not an MP but this would no longer be the case if he went on to beat Reform UK in what is expected to be a tight contest.

In a series of interviews from his prospective new constituency on Saturday, Mr Burnham failed to say that he had confidence in Sir Keir as leader of the party.

Instead, he responded: “I’ve always worked with him and I do have confidence in him as a person.”

Vowing to reclaim the party so it better served working-class and northern voters, Mr Burnham added that he wanted to “save Labour” from what it had become.