Fears are growing for the police investigation into whether Lord Peter Mandelson shared confidential information with paedophile billionaire Jeffrey Epstein.

Reports claim the probe into the former foreign secretary has stalled without the US authorities granting access to the unredacted Epstein files.

According to The Telegraph, neither the Department of Justice nor the FBI has yet agreed to requests from the Metropolitan Police for the documents.

Scotland Yard detectives initially made the request under an informal agreement to share information between law enforcement agencies. This was later escalated to a formal request for mutual legal assistance (MLA), but it could take up to a year to access the documents and there is no guarantee the DoJ will release them.

The Met is investigating claims the Labour grandee passed on market-sensitive information to Epstein during his time as business secretary. The 72-year-old, who was sacked from his post as ambassador to the US last year and resigned from the House of Lords in February, has previously denied any wrongdoing.

He was arrested on suspicion of misconduct in public office on 23 February and his properties were searched. It came several weeks after the DoJ released 3 million documents relating to the late billionaire on 30 January.

However, some information in the exchanges had been redacted to protect victims and avoid jeopardising ongoing investigations.

The arrest followed a tip-off from Sir Lindsay Hoyle, the Commons Speaker, that Lord Mandelson could flee to the British Virgin Islands.

Scotland Yard previously confirmed it was seeking further details from law enforcement partners, including in the US, with reports in March claiming that Met commissioner Sir Mark Rowley was due to press the US authorities on the issue during a visit to Washington.

It is now feared that the investigation could eventually collapse without access to the unredacted documents, according to reports in The Times and The Telegraph. Although there is hope a sufficient case can be built by interviewing former politicians and officials, the files are understood to be crucial to the probe.

Reports have suggested that the Trump administration is hesitant to hand over any files that could cause damage to the president’s reputation or risk future scandals, however US officials have insisted they are simply following established legal procedures.

A DoJ spokesperson told The Telegraph: “The Department of Justice has not refused to assist any jurisdiction investigating potential criminal conduct related to Jeffrey Epstein.

“Both US and UK authorities follow established and legally required procedures for sharing information and evidence, and those processes ensure that any co-operation adheres to applicable laws that govern international evidence sharing and protects the integrity of ongoing matters.”

The Metropolitan Police declined to comment.