The government had signalled it would release most of the documents following revelations about Lord Mandelson's relationship with convicted paedophile Jeffrey Epstein.
Tap here for the latest on the Epstein files
But the prime minister's original plan was for his top civil servant to determine whether any should remain secret on national security grounds, or because they could prejudice international relations.
He was forced into a climbdown after interventions from senior Labour MPs during a dramatic Commons session on Wednesday, including former deputy prime minister Angela Rayner, while Conservative leader Kemi Badenoch accused Sir Keir of an attempted "cover-up".
MPs eventually backed a compromise that will see parliament's Intelligence and Security Committee determine what should be done with the more sensitive files - but it leaves Sir Keir in the most perilous position of his premiership.
Sky News political editor Beth Rigby described the mood in parliament as a "tinderbox", with one senior ally of the prime minister unwilling to rule out resignations from government.
"Temperatures are running high," they said.
Police probe delays release of files
Despite the Commons drama, it is unclear when any documents will be shared with parliament and published by the government amid a police investigation into Lord Mandelson for misconduct in public office.
The Metropolitan Police said it had advised the government "the release of specific documents could undermine our current investigation". "We therefore asked them not to release certain documents at this time," the force added.
Rigby said there is "deep frustration" inside Number 10 about the situation, as it's hoped the release of the files will support the prime minister's assertion that Lord Mandelson repeatedly lied to him about the depths of his relationship with Epstein.
"But with their hands tied, and the mood this febrile, the prime minister is in a precarious position," she added.
Starmer: I regret appointing Mandelson
Downing Street has conceded that the prime minister was aware of Lord Mandelson's links to Epstein when his appointment as US ambassador was confirmed early last year.
Speaking at Prime Minister's Questions, Sir Keir insisted a due diligence process had taken place, but said: "What was not known was the depth, the sheer depth, and the extent of the relationship."
"He lied about that to everyone for years, and new information was published in September showing the relationship was materially different from what we'd been led to believe," he told MPs.
"When the new information came to light, I sacked him."
He added: "I regret appointing him. If I knew then what I know now, he would never have been anywhere near government."
Sir Keir is set to face questions from the media today about the crisis engulfing his administration, after he gives a speech about plans for investment in the UK's most deprived communities.
How did we get here?
The scandal erupted again last Friday when the US Department of Justice published a tranche of over three million Epstein files documents, which included emails that appear to show Lord Mandelson shared sensitive internal government information with the financier while serving in Gordon Brown's government.
It led to the Metropolitan Police opening its investigation into Lord Mandelson for alleged misconduct in public office, which followed referrals from both the Cabinet Office and Mr Brown.
Lord Mandelson resigned his membership of the Labour Party on Sunday. He denied any record or recollection of the payments, but said he did "not wish to cause further embarrassment" to the party.
Sky News has approached representatives for Lord Mandelson for comment.
Being named in the Epstein files is not a sign of wrongdoing, and Lord Mandelson has expressed regret about his past ties to the paedophile, saying in a statement: "I was wrong to believe Epstein following his conviction, and to continue my association with him afterwards. I apologise unequivocally for doing so to the women and girls who suffered."
Lord Mandelson has not responded to the latest allegations. However, in an interview with The Times carried out last week, but published on Monday, he referred to a "handful of misguided historical emails, which I deeply regret sending", and described Epstein as "muck that you can't get off your shoe".
The authenticity of the picture, which shows Andrew with his arm around Ms Giuffre, had previously been questioned by the former Duke of York, who claimed in 2019 that he could not have been in the photo as he was at a Pizza Express in Woking at the time.
However, an email from Maxwell to Jeffrey Epstein, part of the latest files release by the US Department of Justice, appears to confirm the circumstances of the picture.
Dated 10 January 2015, the email contains a "draft statement" in which Maxwell defends herself against allegations of abuse by an unidentified woman.
The name of the woman has been redacted, but - while it cannot be certain - the details indicate it is Ms Giuffre.
Maxwell wrote: "In 2001 I was in London when [redacted] met a number of friends of mine including Prince Andrew. A photograph was taken as I imagine she wanted to show it to friends and family."
Sky News has reached out to Andrew for comment.
Tap here to see the redacted email in full
Ms Giuffre, who died by suicide last April, alleged Andrew had sex with her when she was 17 and claimed she had been trafficked by Epstein.
Andrew has always denied the claim and reached an out-of-court settlement with Ms Giuffre in 2022, which contained no admission of liability or apology.
In 2015, Ms Giuffre filed a civil defamation claim against Maxwell, Epstein's ex-girlfriend and long-time associate, which was settled two years later.
Alleged threesome with stripper
A separate document contained in the latest Epstein files release claims Andrew and Epstein engaged in a threesome with an exotic dancer.
A legal letter from 23 March 2011 alleges Epstein introduced the dancer to the former prince.
The men "then told my client they wanted to have a threesome" and they "prevailed up her to engage in various sex acts".
A later section of the letter refers to the men "satisfying themselves".
Sky News has approached Andrew for a response to this specific claim.
He has vigorously denied any accusations against him related to Epstein and his crimes.
He said in 2019 he regretted his "ill-judged association" with Epstein and sympathises with everyone affected.
Earlier this week, Andrew moved out of Royal Lodge to a house on Sandringham Estate, believed to be temporary accommodation ahead of a permanent move to Norfolk.
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Peter Mandelson, another high-profile British figure named in the latest in the latest tranche of documents, is the subject of a Metropolitan Police investigation over claims he leaked highly sensitive information to Epstein while in public office.
Sir Keir Starmer will be forced to publish files about his decision to appoint him as the UK's US ambassador after Labour backbenchers forced a government climbdown on Wednesday.
Both involved sex, call girls, lurid revelations and a police investigation.
Tap here for the latest on the Epstein files
The Profumo scandal brought down Tory prime minister Harold Macmillan in the early 1960s.
Secretary of state for war John Profumo had an affair with call girl Christine Keeler, who was also involved with a Soviet naval attache.
Profumo lied to parliament about his affair, Macmillan's handling of the crisis was seen as hopeless - and he failed to confront Profumo about the affair.
Months later, Macmillan was gone. Could it happen again?
Now, after an excruciating Prime Minister's Questions, followed by a chaotic Commons showdown on Mandelson, senior MPs are predicting the current scandal will bring down Starmer.
'It's absolutely inevitable'
"The Profumo affair brought down Harold Macmillan," SNP Westminster leader Stephen Flynn told Sky News. "This will bring down Keir Starmer.
"It's absolutely inevitable. Today he chose to be clear, and revealed to the nation what he knew and when. And in doing so he showed a clear lack of judgement, which has broken trust with the people of these isles.
"That's unforgivable for a prime minister, and it's ultimately going to lead to his departure from No 10."
But Flynn isn't alone with his astonishing prediction. His ally Liz Saville-Roberts, Plaid Cymru's Westminster leader, told Sky News: "A number of people are comparing this to the Profumo scandal.
"And, of course, these scandals start slowly and then they speed up. We're seeing it speed up now."
Read more:
What is misconduct in a public office?
Mandelson had no alternative but to resign
Epstein files: Key findings so far
That's the view from the prime minister's opponents, of course.
And it must be said that the Commons debate on a Tory demand for the release of a Mandelson "paper trail" ended with the government's last-minute compromise being approved "on the nod", and MPs of all parties claiming it was a good outcome.
A last-minute government amendment on a scrap of paper gave parliament's Intelligence and Security Committee (ISC) the power to vet which sensitive documents about Mandelson should be released, and which shouldn't.
Rayner's ominous intervention
The government's previous position, that "papers prejudicial to UK national security or international relations" should be kept secret, incensed MPs of all parties, and the PM was heading for a humiliating rebellion and possible defeat.
Ominously for the PM, it was Angela Rayner, his former deputy now banished to the back benches after her stamp duty dodge, that forced him into a U-turn.
There was a sharp intake of breath from MPs as the rose to her feet and made what sounded like a perfectly sensible proposal. The ISC should look at the papers, in "keeping public confidence in the process", she said.
But MPs are nothing if not conspiracy theorists. Was she signalling she might vote with the Tories? Was she twisting the knife? Or was she being helpful? Probably all three.
By the end of the debate, many gloomy Labour MPs were in despair at Sir Keir's faltering and unconvincing performance at PMQs, and the shambolic government U-turn on publishing the Mandelson files.
Was the red queen serving notice that she's ready to seize Starmer's crown? Certainly, his terrible judgement in appointing Mandelson as US ambassador has left him even more vulnerable than ever to a leadership challenge.
And the Mandelson-Epstein furore is suddenly being compared by MPs to another sex and secrets scandal that brought down a prime minister more than 60 years ago.
In an emotional video message posted on social media, the NBC anchor, flanked by her siblings, said: "We are ready to talk. However, we live in a world where voices and images are easily manipulated.
"We need to know without a doubt that she is alive and that you have her. We want to hear from you, and we are ready to listen. Please reach out to us."
Nancy Guthrie was last seen at her home near Tucson, Arizona, on Saturday evening. The 84-year-old was reported missing the following day after she failed to appear at church.
Investigators said they had found signs of forced entry at her home and believe she was taken against her will.
Several media organisations reported receiving apparent ransom notes earlier this week that they handed over to police. Authorities are yet to confirm if these are legitimate.
No suspect or person of interest has been identified, according to Pima County sheriff Chris Nanos.
Mr Nanos previously said the disappearance of Nancy Guthrie, who has limited mobility and requires daily medication, was not "dementia related".
"She's as sharp as a tack," he said. "The family wants everyone to know that this isn't someone who just wandered off."
In the video clip, a tearful Savannah Guthrie, joined by her sister Annie and brother Cameron, said: "Our mum is our heart and our home. She is 84 years old. Her health, her heart, is fragile. She lives in constant pain. She is without any medicine. She needs it to survive, she needs it not to suffer.
"Mummy, if you are hearing this, you are a strong woman. You are God's precious daughter."
Trump sends message of support
Shortly after the video was posted, Donald Trump wrote on Truth Social: "I spoke with Savannah Guthrie, and let her know that I am directing ALL Federal Law Enforcement to be at the family's, and Local Law Enforcement's, complete disposal, IMMEDIATELY.
"We are deploying all resources to get her mother home safely. The prayers of our Nation are with her and her family. GOD BLESS AND PROTECT NANCY!"
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Savannah Guthrie co-hosts Today, the morning show on NBC News, the US sister network of Sky News.
She often brought her mother on as a guest. Speaking on the show in 2022 on Nancy Guthrie's 80th birthday, she said: "She has met unthinkable challenges in her life with grit, without self-pity, with determination and always, always with unshakeable faith.
"She loves us, her family, fiercely, and her selflessness and sacrifice for us, her steadfastness and her unmovable confidence is the reason any of us grew up to do anything."
Of all the security agents chosen to protect the official US delegation, ICE is in Milan for the expected opening ceremony visits by vice president JD Vance and secretary of state Marco Rubio.
They are the Immigration and Customs Enforcement personnel called a "militia that kills" by Milan mayor Beppe Sala following the deaths of two Americans last month in Minneapolis.
There have been attempts by the Italian government to allay fears about their deployment, insisting they won't have powers to conduct policing in the streets.
But just their presence here has been a concern for protesting locals in Milan.
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Add in how tensions have been stoked in recent weeks between Mr Trump and Europe over his threats to capture Greenland, and it all raises the potential for a hostile atmosphere greeting American officials and athletes in the opening ceremony at the San Siro home of AC and Inter Milan on Friday night.
So, I asked International Olympic Committee (IOC) president Kirsty Coventry: would jeering be freedom of expression, or is there a need for spectators to show respect?
"I hope that the opening ceremony is seen by everyone as an opportunity to be respectful of each other," Ms Coventry said, reflecting on seeing athletes from different countries mixing in the official Olympic village in Milan.
"It was a real opportunity to put into perspective how we could be.
"And so I hope that the opening ceremony will do that and will be a reminder for everyone how we could be."
US Games on the horizon
Ms Coventry is yet to meet Mr Trump despite the Los Angeles Olympics being just two years away.
But Olympic chiefs are facing pressure from IOC members in Africa to tackle concerns about the impact of Mr Trump's travel bans on delegations.
Officials from Ethiopia and Djibouti challenged LA 2028 chiefs during meetings in Milan about the need for equal access for all countries to the games - beyond athletes.
Ms Coventry's own Zimbabwe is subject to restrictions for some citizens for entry to the US.
Her lack of contact with Mr Trump after a year leading the IOC contrasts with the US leaders' regular meetings with FIFA president Gianni Infantino, although his World Cup is sooner - coming this summer.
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All you need to know about the Winter Olympics 2026
For now, the IOC moving towards a ban on transgender women competing in women's sport is a policy that will placate Mr Trump.
And Ms Coventry has said: "As we get closer to the Olympics you will see the relations continue… and only get stronger."
But first she has to get through a Winter Olympics that could be a tricky and challenging environment for American athletes in Milan-Cortina.