The man behind Sir Keir Starmer's rise to power finally stepped out of the shadows on Tuesday.

Morgan McSweeney, the Prime Minister's ex-chief of staff, answered questions from Parliament's foreign affairs committee about his role in Peter Mandelson's selection as US ambassador.

His four hours of evidence came after former Foreign Office mandarin Sir Philip Barton faced MPs. This is what we learned.

McSWEENEY TAKES THE BLAME

Mr McSweeney opened his evidence with a brief personal statement in which he tried to shift the blame for Mandelson's appointment away from Sir Keir.

'The appointment of Mandelson as ambassador was a serious error of judgment,' he said. 

'I advised the Prime Minister in support of that appointment and I was wrong to do so. As I said in my resignation statement, I resigned because I believe responsibility should rest with those who make serious mistakes. Accountability in public life cannot apply only when it is convenient.

'The Prime Minister relied on my advice and I got it wrong.'

THE SECRET MEETING

It emerged Sir Keir made the decision to pick Mandelson as US ambassador at a meeting with his aides on or around December 15, 2024 – days before it was announced.

The other attendees were national security adviser Jonathan Powell and the Prime Minister's private secretary Nin Pandit.

MPs were told that the four debated the pros and cons of the appointment before the decision was made.

DID MANDELSON TELL TRUTH?

The Prime Minister asked Mr McSweeney to quiz Mandelson on his friendship with Jeffrey Epstein after due diligence documents warned they were 'particularly close'.

The former chief of staff suggested initially he did not fully believe him, saying: 'I didn't feel that I got (the truth) back from him. But it wasn't my decision. It was the Prime Minister's decision and he saw the DV (developed vetting) as part of that decision.'

But he later said he 'thought he had told the truth' and would never have allowed the appointment if he thought Mandelson might be lying.

KNIFE THROUGH SOUL

Describing his horror when it emerged in September 2025 that Mandelson had been far closer to Epstein than he claimed, Mr McSweeney said 'it was like a knife through my soul'.

The peer had told the paedophile 'I think the world of you' just before he was jailed for soliciting sex from a minor, Bloomberg revealed. 

Mr McSweeney said the truth 'was way, way, way worse than I had expected at the time, and it was when I saw the pictures, when I saw the Bloomberg questions in September 2025, I have to say it was like a knife through my soul'.

SECOND THOUGHTS

He suggested some ministers and officials are re-writing history by claiming they warned against appointing Mandelson.

He said: 'If everyone else was opposed to this appointment but me, (Sir Keir) would not have made it.' But he added: 'I could see that there were pros and cons in the appointment and I worried it would go wrong, so I didn't try to push anything through.'

NO VETTING CONCERNS

Mr McSweeney admitted it would have been 'very embarrassing' if Mandelson had failed his vetting after being appointed, but said there was 'no Plan B'.

He added that, despite well-known concerns about Mandelson's links to Epstein, China and Russia, the question of whether he would pass vetting 'did not jump out to me as a problem'.

WHY CHOOSE HIM?

The former chief of staff said the idea of appointing the peer to Washington was first suggested 'by Mandelson himself'.

And he revealed Sir Keir decided in opposition he wanted to make a political appointment to the role, but waited until after the US presidential election in 2024 to do so. 

Due diligence was carried out on both Mandelson and former Tory chancellor George Osborne, he explained, with the former winning approval because of his experience in trade negotiations.

NOT MY HERO

Mr McSweeney denied reports he was in thrall to Mandelson.

He acknowledged he had grown close to the New Labour grandee, but said he did not regularly seek his advice until 2021.

'I didn't regard him as my mentor,' he added, and also denied claims Mandelson was his 'hero'.

OTHER AMBASSADOR

Downing Street tried to find an ambassadorial role for ex-Labour spin chief Matthew Doyle, Mr McSweeney revealed. But he denied this amounted to 'jobs for the boys', saying it was good management for Sir Keir to try to find a 'softer landing'.

THE MISSING PHONE

Mr McSweeney denied he had deliberately given the police the wrong address when his mobile phone was snatched in the street.

'I was adrenalised, and if I gave any wrong direction, it wasn't intentional,' he said. The theft in October last year has led to fears many messages around Mandelson's appointment may be lost. But Mr McSweeney suggested they were handed to No 10.

FAIT ACCOMPLI

In his earlier session with MPs, Sir Philip Barton revealed he was not asked whether Mandelson should be picked.

He said: 'At no point did anyone consult me, ask me. I was presented with a decision and told to get on with it.' He also admitted he was 'worried'.

THERE WAS PRESSURE

Sir Philip agreed with other Foreign Office figures there was pressure to process Mandelson's clearance as quickly as possible.

But the mandarin said there was no pressure 'on the substance' of the DV decision, although there were demands from No 10 to get the ambassador in place rapidly.

'FIT AND PROPER PERSON'

The Cabinet Office initially claimed because Mandelson was a peer, he was classed as a 'fit and proper person' so did not require DV. But Sir Philip said he raised concerns and the Cabinet Office eventually backed down.

NOT NORMAL PROCESS

In another blow to Sir Keir's claim due process was followed, Sir Philip said the 'normal order' in ambassadorial appointments is 'vetting then announcement'.

Asked what happened in Mandelson's case, he said the timing was 'driven and decided by No 10'.

LAMMY'S WORRIES

Sir Philip also confirmed reports the then-foreign secretary David Lammy shared his concerns about the appointment.

Mr Lammy told him 'he would talk to No 10' at the time.