Three members of the new cabinet have told the BBC that if Labour does not keep its promises, voters will back populists instead.

Chancellor Rachel Reeves suggested it would be an “institutional failure” if they could not get things done.

Interviewed for a Panorama special, the chancellor, foreign secretary and health secretary all warned separately that the public has lost faith in mainstream politics and that if they fail, voters will turn toward the far-left or far-right.

Ms Reeves said that if Labour doesn’t stick to its word, “it will be seen as sort of an institutional failing, that mainstream politics doesn’t deliver.

“And there will be a shift to the populists on the left and right”.

She added Labour had to combat a view among some voters that “politicians are all liars”.

Wes Streeting, the health secretary, who came within 500 votes of losing his seat to a pro-Palestinian campaigner, said: “Unless we deliver, people will lose hope and they will turn to the siren voices of populism.

“So I feel that heavy weight on our shoulders.”

The new Foreign Secretary, David Lammy, said members of the cabinet had to preserve their connections to working class communities and the constituencies they represent.

“We have got to retain that and really be connected to working people”, he said.

“If we don’t, as we’re seeing in other parts of the world, in democracies, the populists – whether from the far-right or the far-left – will offer a different vision.”

Panorama has been behind the scenes with Ms Reeves, Mr Lammy and Mr Streeting in their first fortnight in government, with access to some of their first meetings with officials in Whitehall and ministerial visits.

They tell of how they felt when the exit poll – which pointed to a massive Labour victory – was released, and what it was like to take their seats around the Cabinet Office table for the first time.

Mr Lammy, who was part of Sir Keir Starmer’s leadership campaign back in 2020, said he never worried about the Labour leader’s ability as a potential prime minister.

Rather, he was concerned about whether he could turn around the Labour Party after its shattering defeat in 2019 – believing it would take 10 years, not five.

Now the foreign secretary, who had previously been very critical of Donald Trump, he said he would “embrace the constraint” of being an office-holder where he could no longer speak freely like a backbencher.

The programme also captures the Deputy Prime Minister, Angela Rayner, joking with a group of builders that Ms Reeves is the “moneybags” and she is “tightfisted”.

Reeves responds: “I’m a Yorkshire MP… We have a reputation in Yorkshire of being good with money.”

Moving into Downing Street at the weekend, the chancellor said it was a “big change” for her whole family, but that her husband had been unpacking most of the boxes so far.

Meanwhile, Mr Streeting promised that patients will see a difference in standards in the NHS within a year.

All three cabinet ministers know only too well the risks if they do not keep their promises.

The health secretary admits he is concerned about being able to stick to the targets he has set for 2025.

“I’m worried [that] if we don’t get this right, future generations will curse us. And that is why, in opposition, we did a lot of the heavy lifting, a lot of the serious work to be ready for this moment.”

Labour in Power: Inside the New Government will be broadcast on BBC One at 20:00 tonight.