Peter Mandelson is facing mounting calls to resign as Britain’s ambassador to the United States after British media reported that he worked with convicted sex offender Jeffrey Epstein on a deal involving a taxpayer-owned banking business in 2010.

Reports say emails and court documents show Epstein advised Mandelson during the sale of an energy trading arm of the Royal Bank of Scotland to JP Morgan, a transaction valued at about £1 billion. The correspondence and other material published by U.S. congressional investigators also include a personal message in which Mandelson described Epstein as his “best pal.”

The revelations, drawn from a 10-page birthday album compiled by Ghislaine Maxwell and published by the U.S. House Oversight Committee, include photographs of Mandelson with Epstein and notes in which Mandelson praised Epstein as a close friend. British media reports said Epstein introduced Mandelson to Jes Staley, then a senior JP Morgan banker, and that Epstein arranged meetings between Mandelson and Staley in Davos and New York. Two weeks after one reported Davos meeting in 2010, the sale was announced.

Victims of Epstein’s abuse and some members of Parliament have demanded Mandelson’s dismissal. Sarah Ransome, who has said she was abused by Epstein, told reporters Mandelson was “unsuitable” to hold the ambassadorial post and should be sacked. Conservative MPs have called for a full investigation into Mandelson’s links with Epstein and whether the financier profited from the JP Morgan takeover of Sempra Commodities’ trading arm, part-owned at the time by the taxpayer through RBS.

Mandelson was appointed Britain’s ambassador to the United States by Prime Minister Keir Starmer in February. He has previously acknowledged regret about his association with Epstein. When questioned earlier this year about the relationship by the Financial Times, Mandelson responded angrily to the interview and later said he regretted “even more the hurt” Epstein had caused to young women.

Court papers and media reports say Epstein, who had been convicted and served a sentence in Florida for soliciting a minor before the 2010 deal, introduced Mandelson to people in his financial circle and that Mandelson had visited Epstein properties, including his private island. Some accounts allege Mandelson stayed at Epstein’s Manhattan townhouse while Epstein was serving his sentence; Mandelson has said he wishes he had never met Epstein.

JP Morgan and Mandelson declined to comment on the new reports. The bank has previously said it co-operated with regulators and took action when concerns about individual conduct arose. Jes Staley, who later faced disciplinary action over his dealings with Epstein, was not immediately available for comment.

The material published by U.S. congressional investigators is part of a broader review of Epstein’s network of acquaintances and the role that some associates played in his business and social dealings. Ghislaine Maxwell, who compiled the album, was convicted in the United States of sex trafficking and is serving a prison sentence.

The revelations revive scrutiny of the relationships between prominent public figures and Epstein, and raise fresh questions about the handling of the RBS asset sale more than a decade ago. RBS, majority-owned by the U.K. taxpayer after the 2008 financial crisis, sold its commodities and energy trading arm in the years that followed as part of a wider restructuring.

Labour’s leadership has not publicly announced any immediate disciplinary steps. Tory MPs urged the government to launch an inquiry to establish whether any improprieties occurred and whether proper transparency was observed in the sale of public assets.

The House Oversight Committee’s release of the Maxwell-compiled album has prompted renewed demands for documents and testimony relating to Epstein’s contacts with politicians and bankers worldwide. Investigators and campaigners for Epstein’s victims say the material underscores the extent of his contacts in high places and call for full disclosure of related communications.

Mandates for further oversight or formal investigations would be decided by government authorities and parliamentary committees. For now, the revelations have placed Britain’s ambassador in Washington under intense public and political pressure at a sensitive time in U.K.-U.S. relations.