British police investigating the former prince Andrew and Peter Mandelson are preparing to start interviewing witnesses in Royal and government circles.

It comes as police fear that prosecutors will be “reluctant” to bring charges unless the Trump administration agrees to hand over the original documents from the Epstein files.

The two police forces that have launched full criminal investigations as a result of revelations in the Epstein files have been in discussions with the special crime division of the Crown Prosecution Service (CPS), which authorises criminal charges in England and Wales.

Thames Valley police is investigating Andrew Mountbatten-Windsor, King Charles’s brother, for misconduct in public office, over claims sensitive material was passed to Epstein while he was serving as a UK trade envoy.

The Metropolitan police is investigating the former Labour grandee Peter Mandelson for misconduct in public office over claims he passed on sensitive information while a cabinet minister to Epstein.

Both men have been arrested and released and are understood to deny wrongdoing.

So far, redacted documents relating to the disgraced financier and sex offender Jeffrey Epstein and his associates have been published on the US Department of Justice website.

The DoJ, seen as being under Trump’s control, has told British police it will not consider handing over the original documents without a formal request being made. That is a bureaucratic and lengthy process.

Efforts by British police – including informal requests to US officials by Met commissioner Sir Mark Rowley – to get the documents without going through a mutual legal assistance request have been unsuccessful.

The Met has now sent a formal request to the US authorities for the original and unredacted documents from the Epstein files as part of their investigation into Mandelson, the former British ambassador in Washington.

One source said: “It is difficult to make anything stick without those documents. The US could have handed them over without making [British police] go down the formal route.”

A senior source added: “It is very difficult for [CPS] to authorise prosecutions with the material as it is.” Another source said: “A lot rests on having the originals. It makes it significantly more difficult.”

Formal interviews of witnesses in Royal circles and government circles are expected to start shortly as part of both criminal investigations.

For Mandelson it will be former and current senior people in government, including officials, and potentially including former prime minister Gordon Brown, who has already written to the Met about his concerns regarding Epstein.

A national gold group hosted by the National Police Chiefs Council met again this Thursday. It is coordinating British police efforts to investigate allegations in the Epstein files.

British police forces are also considering whether flights linked to Epstein that arrived and took off from British airports merit a full criminal investigation, in case they were trafficking women into the UK for abuse.

The six forces considering claims about the Epstein flights into airports in their area are Norfolk, Essex, Bedfordshire, West Midlands, the Met and Police Scotland.

The gold group has appointed a senior detective to spearhead its efforts, with analysts seconded and staff at the National Crime Agency also helping.

The CPS declined to comment, as did the NPCC, which is coordinating replies to media inquiries on behalf of all forces.

On Friday the European anti-fraud office, known as OLAF, said it was investigating Mandelson, confirming its investigation covers his time serving as an EU trade commissioner from 2004 to 2008.

A spokesperson said: “OLAF can confirm the opening of an investigation on Mr Mandelson. However, as the investigation is ongoing, we cannot issue any further comment or statement.

“This is in order to protect the confidentiality of ongoing and possible ensuing investigations, possible subsequent judicial proceedings, personal data and procedural rights.”

Also on Friday the BBC claimed that Epstein housed some of his alleged abuse victims in flats in London, with six women accusing the late financier of sexually abusing them.

Some of the women were brought to the UK after the Metropolitan police declined to investigate allegations from Virginia Giuffre’s in 2015 that she had been a victim of trafficking to London.