Gordon Brown called for police to investigate whether Andrew Mountbatten-Windsor used tax-funded aircraft and RAF bases to arrange meetings with Jeffrey Epstein, it has emerged.
The "shocked" former Prime Minister had sent a series of letters to six police forces this week.
These were addressed to authorities in London, Surrey, Sussex, Thames Valley, Norfolk and Bedfordshire.
Mr Brown said the correspondence contained "new and additional information" over the ex-prince after he warned of the "biggest scandal of all".
The letters reveal his serious concerns that Mr Mountbatten-Windsor may have used chartered RAF flights for personal engagements - potentially involving Epstein.
Mr Brown also fears the former prince may have leaked confidential information from official trips in what he describes as a "wholly unacceptable" use of public funds.
Mr Mountbatten-Windsor served as a trade envoy from 2001 to 2011.
During this time, he earned the nickname "Airmiles Andy" for taking taxpayer-funded flights on private trips.
Mr Brown suspects these aircraft may have facilitated meetings between the two men, The Telegraph reported on Saturday.
His concerns extend to a December 2000 incident when Epstein's Gulfstream jet landed at RAF Marham in Norfolk.
US Department of Justice records show the aircraft first arrived at Luton Airport on December 6 carrying both Epstein and Ghislaine Maxwell.
Gordon Brown called for police to investigate whether Andrew Mountbatten-Windsor used tax-funded aircraft and RAF bases to arrange meetings with Jeffrey Epstein
| GETTYThe following day, it flew 80 miles to the military base with two additional passengers, including an unnamed female.
From RAF Marham, Epstein and Maxwell travelled 20 miles to the Queen's Sandringham Estate.
Mr Mountbatten-Windsor allegedly arranged their access to the base and entertained them there.
Mr Brown's letter references a photograph showing the then-prince lying across guests' laps at Sandringham, with Maxwell beside him.
He now wants police to question officials from four Government departments - the Ministry of Defence, Department for Transport, Foreign Office and Treasury - about the trade envoy role.
The ex-PM is looking to establish any connection between Mr Mountbatten-Windsor's official duties and the paedophile financier.
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Mr Mountbatten-Windsor allegedly arranged Jeffrey Epstein and Ghislaine Maxwell's access to RAF Marham and entertained them there
| REUTERSMr Brown has compiled a list of British runways used by Epstein, covering airports in Edinburgh, Belfast, Liverpool, Birmingham, Norfolk, Gatwick, Heathrow, Luton and Stansted.
He believes airline staff at these nine airports should face questioning about Epstein's flights.
Mr Brown has requested that MoD records also be handed to investigators.
And he is pushing for police to examine what background checks were conducted on Epstein before he was permitted to land.
Mr Brown has already called the state's "unacknowledged role" in the Epstein affair "by far the biggest scandal of all".
Gordon Brown has urged that Ministry of Defence records be handed to investigators
| GETTYMr Mountbatten-Windsor was arrested on Thursday on suspicion of misconduct in a public office.
He has denied any wrongdoing over his Epstein links, but has not directly responded to the latest allegations.
His arrest followed the release of emails allegedly showing he passed sensitive information to Epstein while serving in his Government role.
Mr Brown believes the use of hundreds of thousands of pounds in taxpayer money for trade envoy flights may worsen the severity of any misconduct.
The King removed his titles last year - before Downing Street made an unprecedented intervention on Friday, raising the prospect he could lose his place in the line of succession.
Police continued searching Royal Lodge, his former home, on Saturday.
An MoD spokesman said private aircraft using RAF airfields was "standard practice", subject to fees and approval based on security and operational considerations.