The Metropolitan Police’s investigation into Lord Peter Mandelson is reportedly on the brink of collapse after US authorities ignored requests for information.

The former US Ambassador faces charges of misconduct in public office over allegations he passed confidential information to the late paedophile financier Jeffrey Epstein during the 2008 financial crisis.

But in order for Scotland Yard to properly investigate, detectives believe they need access to the unredacted Epstein files.

The US Department of Justice (DoJ) and FBI have so far ignored the Met’s request for the documents, The Daily Telegraph reported.

The appeal was initially made under an informal agreement between the organisations to share information, but the Met is said not to have received an acknowledgement.

British police have now escalated their request through the formal mutual legal assistance process, which could take years.

It means Lord Mandelson’s lawyers could also argue that emails currently held by police are partly redacted, do not provide a complete picture and prosecuting the peer based on their contents would be unfair.

The Met is understood to be gathering evidence in other ways, including speaking to former colleagues.

However, misconduct in public office is a notoriously difficult crime to prosecute and requires substantial documentary evidence to secure a conviction.

A DoJ spokesman 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 department remains committed to co-operating with all jurisdictions pursuing potential crimes and will continue to do so in accordance with federal law and longstanding practice.”

Lord Mandelson was sacked as US ambassador in September last year as a result of his links with Epstein.

Leaked emails showed the peer sent supportive messages to the paedophile even as he faced jail for sex offences.

Lord Mandelson has always denied any wrongdoing and said he regrets his friendship with Epstein.