Sir Keir Starmer has backed Rachel Reeves to remain chancellor “into the next election and for many years after” after she was seen crying during Prime Minister’s Questions.

The prime minister had refused to say whether Reeves would remain in her job until the next election in front of MPs in the Commons, during a session in which the chancellor wiped away tears as she sat behind him.

But later Sir Keir told BBC Radio 4’s Political Thinking he worked “in lockstep” with Reeves and she was “doing an excellent job as chancellor”.

After PMQs, Reeves’ spokesperson said she had been dealing with a “personal matter” and Sir Keir insisted her tears had “nothing to do with politics”.

Asked if Reeves would remain in government Sir Keir said: “She’s done an excellent job as chancellor and we have delivered inward investment to this country in record numbers.

“She and I work together, we think together.

“In the past there have been examples – I won’t give any specifics – of chancellors and prime ministers who weren’t in lockstep. We’re in lockstep.”

He said Reeves’ tears had “nothing to do with politics” or this week’s welfare U-turns – which potentially blows a hole in her Budget plans.

“That’s absolutely wrong,” said Sir Keir. “Nothing to do with what’s happened this week. It was a personal matter for her, I’m not going to intrude on her privacy by talking to you.”

At a highly charged PMQs, Conservative leader Kemi Badenoch laid into the government over its welfare U-turns.

She said the chancellor would now be forced to put up taxes “to pay for his incompetence” and asked if she would still be chancellor at the next election.

She said the chancellor “looks absolutely miserable”.

And she told the PM: “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.”

Sir Keir said: “No prime minister or chancellor ever stands at the dispatch box and writes budgets in the future.”

He ignored Badenoch’s questions and instead insisted the welfare reform bill would get more people back into work and blamed Tory “stagnation” for creating the problems it was trying to fix.

Reeves was seen to wipe away tears during the PMQs exchanges.

The extraordinary Commons scenes appeared to unsettle the financial markets, with the pound falling against major currencies and the cost of government borrowing rising.

Many colleagues and allies of Reeves in Parliament are blaming an altercation with the Commons Speaker Sir Lindsay Hoyle for upsetting her.

Several have accused him of having been abrupt with the chancellor in a meeting before PMQs.

It is thought to have been about an interaction they had during Treasury questions on Tuesday in which Sir Lindsay asked her to give shorter answers.

However, no one who the BBC has spoken to is claiming to have witnessed the interaction personally.

The chancellor’s team have declined to comment, as has the Speaker’s office.

Speaking to ITV, Health Secretary Wes Streeting said, “it is easy to forget we are all humans as politicians, and we have lives like everyone else”.

As Reeves left PMQs her sister Ellie Reeves, who is also a Labour MP, took her hand in an apparent show of support.

Following PMQs, Badenoch’s spokesperson said a “personal matter doesn’t really clear it up” as “you normally tell people what the personal matter is”.

Shadow justice secretary Robert Jenrick went further than the Tory leader in a social media video, saying the chancellor’s career was now dead after an “embarrassing” U-turn and it was time for her to go.

But he later added: “I obviously hope that Rachel Reeves’s personal matter is resolved. It’s never nice to see someone upset. The PM had a chance to support her at PMQs but threw her under the bus.”

He said borrowing costs were soaring and the pound plummeting because “the market has lost confidence in the government’s ability to control spending”.

Stephen Flynn, the SNP’s Westminster leader, said: “Like almost all MPs I don’t know why the chancellor was upset in the chamber today, but I do hope she is okay and back to her duties this afternoon.

“Seeing another person in distress is always very difficult, and we are wishing her well.”