Detectives investigating Andrew Mountbatten-Windsor are reportedly seeking files from the Met Police relating to the former prince's accuser Virginia Giuffre.
Thames Valley Police is understood to have made contact with the Met to review its records - and is also keen to speak to the 66-year-old's former protection officers.
Andrew was arrested in February at the Sandringham Estate on suspicion of misconduct in public office, though a charge is yet to be brought.
In a bombshell development, the force announced on Friday that its probe is considering a wide range of offences, including sexual misconduct and corruption.
Giuffre, who died by suicide in April 2025, was paid £12million by Andrew in 2022 after claiming she was sexually assaulted by him three times when she was 17.
Andrew has always denied wrongdoing, but there are allegations that he paid one of his protection officers to dig up dirt on Giuffre after she publicised her allegations in 2011.
The Met, however, denies that the then-prince's alleged request was carried out.
Giuffre was interviewed by officers from the force in 2015, The Times reports, after she complained that she was sex trafficked by Epstein and his partner Ghislaine Maxwell.
Detectives investigating Andrew Mountbatten-Windsor are reportedly seeking files from the Met Police relating to the former prince's accuser Virginia Giuffre (Andrew is pictured after his arrest in February)
Giuffre, who died by suicide last year, was paid £12million by Andrew in 2022
Andrew, Giuffre and Ghislaine Maxwell are pictured together in a photo thought to have been taken in early 2001
But an investigation was never launched because, the Met said, there was no allegation of criminal conduct against any UK-based nationals. It added that any investigation into human trafficking would be focused on activities outside Britain.
The force has reviewed the case on a number of occasions, including after Giuffre's death, but its position remains unchanged.
Officers at Thames Valley reportedly now want to review the files themselves, and are also keen to speak to the Met protection officers who stayed with Andrew at properties owned by Jeffrey Epstein.
Officers are even understood to have been instructed to provide security at the paedophile financier's New York home, according to the US Department of Justice.
The Met insists it never uncovered any evidence of wrongdoing, but detectives want to be confident there are no outstanding inquiries.
Andrew's sensational arrest came more than three months ago, but it's thought detectives are struggling to build a compelling enough case to bring charges.
Thames Valley Police allege that Andrew leaked secrets to Epstein during his decade as the UK's trade envoy, and announced on Friday its probe has broadened.
The force made an appeal to 'victim survivors' to come forward after identifying 'multiple lines of inquiry' in what is being described as a 'significant investigation'.
Police have seized evidence in a raid of Andrew's former home at Royal Lodge, Windsor, and his new property in Norfolk.
Senior officers have spoken to the Crown Prosecution Service for 'early investigative advice' ahead of a potential prosecution, it was reported on Friday.
They are also liaising with the American DoJ to formally request evidence contained in the millions of documents from the Epstein files.
Alongside the allegations from the files, they are assessing separate claims that Epstein sent a woman to the UK for sex with Andrew in 2010, mirroring accusations made by the late Giuffre.
Detectives have spoken to a lawyer for the alleged second victim, who has not been identified, but officers are yet to carry out interviews because she has not made a formal complaint to police.
Assistant Chief Constable Oliver Wright said the force had assembled a dedicated team of its 'most experienced specialist investigators', which include detectives experienced in investigating serious sexual attacks and financial experts.
He confirmed they had spoken to a number of witnesses, but said he hopes others will come forward to shed light on Andrew's relationship with the paedophile.
Thames Valley Police announced last week that its probe is considering a wide range of offences, including sexual misconduct and corruption
'I really want to stress that our door is open. Whenever a victim survivor is ready to engage with us, we're ready for you at whatever point that may be,' the Assistant Chief Constable continued.
'In terms of Epstein victims and survivors, we hope that anyone with relevant information will come forward.'
Describing progress in the investigation, he said: 'We have been working really closely with the Department of Justice Office in the US seeking further information that may be related to this investigation. We have also been working really closely with the CPS.
'There's a number of aspects of alleged misconduct that the investigation is examining so we're speaking with a range of witnesses. We do really want to get the message across that we're encouraging anyone with information to get in touch with us.'
He warned that the inquiry could take months before detectives are ready to submit a file of evidence to the CPS to consider whether to bring criminal charges.
The senior officer added: 'The investigation is by necessity hugely thorough, and will take time. We're proceeding with real care and caution.'
One of the key issues to be determined is whether the former prince can be considered a public officer under the terms of the offence.
Police will have to interview various officials and seek disclosure from the Government of any documents Andrew signed regarding confidentiality in his role, which he held for ten years until 2011.
CPS guidance says: 'There is no simple definition of a public officer, and each case must be assessed individually, taking into account the nature of the role, the duties carried out and the level of public trust involved.'
Public officials include individuals such as police officers, civil servants, judges, elected officials and Army officers.
Emails released in the Epstein dump suggest the former duke shared reports of official visits to Hong Kong, Vietnam and Singapore with the financier. Andrew was the UK's Special Representative for Trade and Investment in Asia in 2010 and 2011.
He is accused of sharing confidential reports and investment opportunities with Epstein after the financier was released from prison on child sex offences in 2009.
One email, in November 2010, was forwarded by Andrew just five minutes after being sent by his then-special adviser, Amit Patel.
Then, on Christmas Eve in 2010, Andrew allegedly looped Epstein in on a confidential briefing about investment opportunities in the reconstruction of Helmand in Afghanistan.
Detectives are now speaking to officials in the Cabinet Office and Buckingham Palace, which has previously released a statement confirming staff stand 'ready to support' police.
Royal aides say the Palace cannot comment while there is an active police inquiry for fear of prejudicing any investigation.
Sources point back to the 'robust' action taken by the King in stripping his brother of his remaining titles and honours and ensuring his departure from Royal Lodge.
Both he and Queen Camilla - who has highlighted issues around violence against women - also said last year that their 'thoughts and utmost sympathies have been, and remain with, the victims and survivors of any and all forms of abuse'.
The King's brother has not addressed the allegations, but has always denied any wrongdoing in his dealings with Epstein or knowledge of his sex crimes.
Misconduct in public office, which carries a potential maximum life sentence, covers a range of offending, including sharing confidential information, sexual misconduct, corruption, fraudulent conduct and dishonesty.