Downing Street refused to say whether other figures in Number 10 had known the full story and chose not to tell Starmer.
Reports at the weekend suggested that after Prime Minister’s Questions last week – when Starmer backed Mandelson publicly – he turned on his chief of staff, telling him: “You are supposed to protect me from things like this”.
McSweeney is said to have responded: “That’s exactly what I was trying to do”.
While No 10 has denied the exchange, McSweeney is facing a growing backlash from within the Labour Party over his role in the scandal.
Here, the Telegraph looks at the timing of the events leading up to the dismissal of Mandelson and the questions that remain unanswered.
‘Birthday book’
The story that led to Mandelson’s downfall broke at the start of last week, when a congressional committee in the US released Epstein’s “birthday book”.
The book, compiled for the financier’s 50th birthday, included a message from Mandelson calling him his “best pal”.
Later in the day, Bloomberg sent a 2000-word email to Mandelson ahead of publishing an article on a cache of old correspondence the outlet had unearthed between the peer and Epstein.
Bloomberg said that the right of reply contained 20 questions, and originally gave him until 5pm last Friday to respond.
But there are still unanswered questions about the events of the day.
It is not known whether Mandelson forwarded the email from Bloomberg to anyone within the embassy, the Foreign Office or No 10.
Neither is it known which quotes from the cache of emails were included in that first approach to Mandelson.
List of questions
It was early on Tuesday local time that the Foreign Office became aware of the emails between Epstein and Mandelson which ultimately led to the ambassador’s dismissal.
Baroness Smith of Malvern, a skills minister, has claimed that “media sources came forward to the Foreign Office with extracts from the emails” on Tuesday.
She said the department then demanded answers from Mandelson. Officials sent a list of questions for the peer to answer.
The Prime Minister’s official spokesman said the Foreign Office made No 10 aware that it had received a media approach and that it was investigating the emails.
The spokesman would not say exactly when Downing Street was told, but it has been reported that Starmer knew on Tuesday, two full days before Lord Mandelson was sacked.
No 10 said the Prime Minister was made aware that there was an investigation, but was not informed about the contents of the emails.
The spokesman would not say whether others in Downing Street knew that the emails contained suggestions from the Labour peer that Epstein’s conviction was wrongful.
If McSweeney did know the full details, he will face questions as to why he did not tell Starmer.
Bloomberg sent a second email to Mandelson after he did not reply to the original inquiry and gave him a new deadline of 10pm on Wednesday.
By the end of the day, the Foreign Office had still received no reply from the peer to their questions.
‘Confidence in the ambassador’
Early in the morning, Mandelson appeared in a video interview with the Sun, responding to his comments in the birthday book and hinting that more “embarrassing” revelations about his relationship with Epstein were to come.
Despite this, Starmer seems not to have asked his officials or the Foreign Office what the nature of the allegations being investigated were.
When Starmer stood at the Commons despatch box for Prime Minister’s Questions Mandelson still had not responded to the Foreign Office questions.
Bloomberg also contacted the peer via WhatsApp on his US and UK numbers, and he replied saying he did not know “what these emails are or where they come from”.
At PMQs, Starmer was battered by an effective performance from Tory leader Kemi Badenoch, who asked him about the Telegraph’s revelation that morning that Mandelson had brokered a £1b deal with Epstein after he had been convicted of child sex offences.
“Given this new information, does the Prime Minister really think that it is tenable for our ambassador to remain in post?” she asked.
The Prime Minister gave Mandelson his total backing, saying: “The relationship between the US and the UK is one of our foremost relationships, and I have confidence in the ambassador in the role he is doing.”
Ministers have insisted that it was only after PMQs, which finish at around 12.30pm, that Starmer became aware of the full details of the emails that Bloomberg would publish.
The outlet said the last time it heard from the Labour peer was at 3.49pm UK time, when he told journalists that he was “taking advice on legalities”.
Olly Robbins, the top civil servant at the Foreign Office, only got a response from Mandelson about the veracity of the emails on Wednesday afternoon.
Starmer was told about the response from the ambassador, and it was on this basis that he decided that Mandelson should go.
Smith told Sky News: “When the full details of those [emails] became available to the Prime Minister last Wednesday afternoon, he very quickly made the decision to remove Peter Mandelson as our ambassador.”
But he did not sack the peer that night, even though he had apparently made up his mind, instead deciding he needed time to think.
There remain questions for government officials about the reasons for the delay in giving the Prime Minister the full information about the emails.
Would he have mounted such a staunch defence of Mandelson had he known what the Foreign Office was investigating?
Third sacking
Only on Thursday morning did Starmer decide to sack Mandelson.
He seems to have been galvanised following a meeting with Yvette Cooper, his newly appointed Foreign Secretary.
Starmer ordered Robbins to inform Mandelson that he was being withdrawn mid-morning UK time.
The Labour peer was awoken at 5.35am in Washington by a security official knocking at his door telling him to get onto a secure phone line.
After he was told his fate, the ex-ambassador waited for advance sight of the Foreign Office’s press notice announcing his departure from the Government, but it never arrived.
The statement was issued to the media, and seconds later Stephen Doughty, a junior Foreign Office minister, told MPs that Mandelson had been withdrawn from the US because “additional information” had come to light about his friendship with Epstein.
For the third time in his life, Mandelson had been sacked from a high-profile government role.
The scandal could not have come at a worse time for Sir Keir, days before Donald Trump is due to arrive in the UK for a state visit today.
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