Lord Mandelson was sacked as ambassador in September 2025, after new information came to light about the depth of his relationship with Epstein.
This included photos of the pair together and supportive emails he sent to Epstein as he faced charges for sex offences in 2008.
McSweeney told the committee that when he saw the revelations “it was like a knife through my soul”.
“The nature of the relationship that I understood he had with Epstein was not a close friendship,” he said.
“How I understood it at the time was a passing acquaintance that he regretted having and that he apologised for.
“What has emerged since then was way, way, way worse than I had expected at the time [of the appointment].”
Before Lord Mandelson was appointed, a due diligence check – a separate process to the security vetting – was carried out by a team at the Cabinet Office and sent to the prime minister.
This flagged Lord Mandelson’s continued relationship with Epstein after his conviction as a potential “reputational risk”.
McSweeney was subsequently asked by the PM to send three follow-up questions to Lord Mandelson about his association with Epstein.
While at the time McSweeney said he believed the answers were truthful, he later realised he was not given the “full truth” and that revelations in the Epstein files showed Lord Mandelson was “unfit” for the job.
Challenged over whether it was appropriate for him to ask the follow-up questions, given he was a friend of Lord Mandelson, McSweeney acknowledged that in hindsight it would have been “much better” for “public appearances” if the Cabinet Office’s propriety and ethics team had done this.
However, McSweeney added that he was not sure the Cabinet Office “would have got better answers”.
