Rachel Reeves admitted she was ‘under so much pressure’ minutes before being reduced to tears in the Commons, triggering a new political and economic crisis.

The Chancellor is said to have made the admission to Speaker Sir Lindsay Hoyle before taking her seat for an extraordinary session of Prime Minister’s Questions.

She was forced to listen in silence as Sir Keir Starmer refused to say in front of MPs that she was secure in her job, as he was battered over his welfare surrender to Labour rebels.

In an extraordinary moment that spooked markets, tears appeared to roll down Ms Reeves’ cheek as Kemi Badenoch demanded a guarantee she would stay in No11 – something the premier did not give.

She was seen being comforted by her sister Ellie – also a Labour minister – as she left the chamber, although Sir Keir did not speak to her.

Ms Reeves’ spokesman insisted afterwards that it was a ‘personal matter’ and he would not be ‘getting into’ the reasons. Downing Street said the Chancellor ‘is going nowhere’, had not resigned, and retains Sir Keir’s ‘full backing’.

No10 and No11 both denied claims Ms Reeves had an argument with Sir Keir before they entered the Commons.

But the Guardian reported that she told the Speaker about the strain she was under.

She apparently broke down when she was privately rebuked by Speaker Lindsay Hoyle for giving long answers during Treasury questions yesterday.

Health Secretary Wes Streeting tonight said Ms Reeves has ‘toughness and hard-headedness… in spades’ as he spoke out in support of the Chancellor.

‘It’s why with the choices she’s made, not always the most popular choices, is creating the conditions for our economy to grow,’ he told ITV’s Peston.

Mr Streeting added Ms Reeves has ‘something going on personally, not professionally’.

‘It’s easy to forget that we’re all humans as politicians and we have lives like everyone else,’ he continued.

Interest rates on 10-year and 30-year gilts – effectively the cost of government borrowing – spiked and the pound slipped sharply against the US dollar as the Commons scenes unfolded earlier.

Just a year on from his election landslide, Sir Keir’s authority has been left in tatters after his extraordinary surrender to avert defeat at the hands of Labour rebels.

Ms Badenoch said he had made ‘mistake after mistake’, highlighting volte faces over grooming gangs and winter fuel allowance. She also pointed to a visibly-upset Reeves, sitting next to the PM, saying she looked ‘miserable’ and was being used as a ‘human shield’.

Last night Sir Keir effectively tore up his benefits reforms, which had been due to shave £5billion a year off spirallling costs by the end of the Parliament – but will now actually increase spending by £100million.

The move heaped misery on Ms Reeves, who was already struggling to fill a black hole in the public finances that could amount to tens of billions of pounds.

Touring broadcast studios this morning, Cabinet Office minister Pat McFadden warned there would be ‘financial consequences’ – hinting that the tax burden will need to rise again.

Ms Reeves has insisted Labour will stick to manifesto pledges of no hikes to income tax, employee National Insurance or VAT. And she had been adamant that she will not break her ‘cast iron’ fiscal rules.

But she refused to guarantee yesterday that the hated freeze in tax thresholds will not be extended.

In highly emotional scenes at PMQs, Ms Badenoch said: ‘This man has forgotten that his welfare bill was there to plug a black hole created by the Chancellor. Instead they’re creating new ones. They’re creating new ones.

‘(Ms Reeves) is pointing at me, she looks absolutely miserable. Labour MPs are going on the record saying that the Chancellor is toast, and the reality is that she is a human shield for his incompetence. In January, he said that she would be in post until the next election. Will she really?’

Sir Keir replied: ‘(Mrs Badenoch) certainly won’t. I have to say, I’m always cheered up when she asks me questions or responds to a statement because she always makes a complete mess of it and shows just how unserious and irrelevant they are.

‘She talks about the black hole, they left a £22billion black hole in our economy and we’re clearing it up, and I’m really proud that in the first year of a Labour Government, we got free school meals, breakfast clubs, childcare, got £15 billion invested in transport in the North and the Midlands.

‘We’re cutting regulation, planning and infrastructure is pounding forward, building 1.5 million homes, the biggest investment in social and affordable housing, and of course the three trade deals.’

Mrs Badenoch replied: ‘How awful for the Chancellor that he couldn’t confirm that she would stay in place.’

Challenged afterwards why Sir Keir failed to give Ms Reeves the vote of confidence, the PM’s press secretary said: ‘He has done so repeatedly.

‘The Chancellor is going nowhere. She has the Prime Minister’s full backing.

‘He has said it plenty of times, he doesn’t need to repeat it every time the Leader of the Opposition speculates about Labour politicians.

‘The Chancellor and the Prime Minister are focused entirely on delivering for working people.

‘It’s thanks to the Chancellor’s management of the economy that we managed to restore stability, which has led to four interest rate cuts, wages rising faster than inflation and she recently delivered a spending review that invested in Britain’s national renewal.’

Asked whether the Prime Minister still had confidence in Work and Pensions Secretary Liz Kendall, the press secretary said: ‘Yes.’

A spokesman for the Chancellor said: ‘It’s a personal matter which, as you would expect, we are not going to get into.

‘The Chancellor will be working out of Downing Street this afternoon.’

Aides to Speaker Lindsay Hoyle refused to comment on claims he had a row with Ms Reeves shortly before the PMQs session began.

But MPs believe Sir Lindsay only rebuked Ms Reeves for giving excessively long answers at Treasury questions yesterday, with the Speaker surprised that she immediate became upset.

The pair had already exchanged words on the subject during the session yesterday.

One MP told MailOnline that the cause was a spat with the PM before that clash. ‘There has been a major row before, just before she walked in. I think it was with Keir,’ they said.

However, both No10 and No11 denied that there was any argument between Ms Reeves and Sir Keir.

After the session, Mrs Badenoch’s spokesman said ‘personal matter doesn’t really clear it up’ and ‘you normally tell people what the personal matter is’.

He added: ‘I’m not going to speculate… I think we should find out what’s going on.’

Labour circles have been in a frenzy over how the Chancellor will handle the crisis in the public finances. One MP said: ‘She is in massive trouble. This government has lost control. It is the worst politics of anybody – it doesn’t matter whether you are left or right.

‘Governments get this after four years, but we’re not even at one year.’

Rather than leaving the Commons immediate after PMQs as usual, Sir Keir remained on the estate for about two hours having meetings.

Meanwhile, rebel ringleaders gloated that they had ‘power’ over the PM and stepped up demands for a lurch to the Left.

Rachael Maskell, whose fatal amendment sparked the benefits shambles, urged a £24billion ‘wealth tax’ to pay for more handouts.

Deputy PM Angela Rayner is said to have brokered the deal with rebels, fueling speculation that she is positioning to succeed Sir Keir. Opponents jibed it is obvious that Sir Keir will not now lead the party into the next election.

Appearing on ITV’s Lorraine show, Ms Rayner insisted she did not want the top job, joking that it would ‘age me by 10 years’.

Told that Sir Keir looked ‘tired’ and ‘exhausted’, she said: ‘It’s a very challenging job. To be fair for Keir Starmer there’s been a lot going on…

‘There’s a lot going on and the PM’s been here there and everywhere doing the job for Britain.’

Amid carnage at Westminster yesterday, the PM’s carefully assembled truce with rebels dramatically disintegrated.

Facing the threat of a massive revolt, Sir Keir opted to make yet another major concession just 90 minutes before the vote.

Ministers pledged that changes to disability handouts will not be finalised until after a review – meaning that the package as it stands will actually make the current system more expensive than before up to 2029.

Sir Keir – who is days away from marking the first anniversary of his election landslide – had already agreed that the benefits curbs would only apply to new claimants.

There was mocking laughter in the chamber as Social Security Minister Stephen Timms was asked how much the proposals would save now, and merely replied that the government would ‘set out figures in the usual way’.

Despite the humiliating manoeuvres, when the vote was held 44 Labour MPs still backed the fatal amendment and others abstained – although it was comfortably defeated by 328 to 149 as Tories largely stayed away.

Shortly afterwards, the Bill cleared second reading stage by 335 to 260, with the rebellion growing to 49. It will now be scrutinised at committee, where there could be further problems.