The man who was once in charge of investigating Jeffrey Epstein has accused British authorities of protecting Prince Andrew, allowing him to avoid a formal interview regarding his friendship with the dead sex trafficker.

Geoffrey Berman was US attorney for the Southern District of New York (SDNY) until June of 2020, almost a year after Epstein's death in prison. He has now written a book, Holding the Line: Inside the Nation's Pre-eminent US Attorney's Office and Its Battle with the Trump Justice Department. Not the catchiest of titles.

Among other subjects, Berman touches on the SDNY's long-running and ultimately fruitless efforts to question Prince Andrew about his relationship with Epstein and co-conspirator Ghislaine Maxwell - awkward timing, given the book has been released while the royal family is in mourning for Queen Elizabeth II.

While Epstein died before he could face trial, in June Maxwell was sentenced to 20 years in prison, having been convicted on sex trafficking charges.

In his account, Berman takes issue with Prince Andrew's public insistence that he was co-operating with the SDNY's Epstein investigation.

Jeffrey Epstein and Ghislaine Maxwell were both charged with enticing and trafficking minors. Prince Andrew had a close friendship with Epstein. Photo / File

"(Prince Andrew) stated publicly that he would co-operate with the investigation, and we intended to give him a chance to make good on his word," he writes.

While Prince Andrew "kept publicly saying that he was co-operating", that was "not true", the former US attorney claims.

After Prince Andrew's trainwreck appearance on the BBC in 2019, Berman asked two members of his office to reach out to his team, to set up an interview.

He alleges his team was hampered at every turn and spent "about two weeks just trying to find out who Andrew's lawyers were".

"We tried calling Buckingham Palace, and they were not helpful," he says.

"We tried the Department of Justice attache and the State Department. No luck.

"When we finally got to his lawyers, they had all these questions. 'What kind of interview will it be? Are there any protections? Is there this, is there that?' And we kept answering, and all that led to further questions, and they're saying, you know, 'We'll consider it.'"

Berman describes the email exchange as "endless".

"It was clear we were getting the run-around," he writes.

"He was not going to sit down for an interview with us, despite assuring the public he was ready, willing and able to co-operate."

Fast forward to January 2020. At a press conference, Berman was asked about Prince Andrew and told reporters there had been "zero co-operation" from the Duke of York.

In the book, Berman says that remark brought Prince Andrew's lawyers "back to the table". But once again, it did not result in an interview.

His office next tried to go through a more formal route, invoking America's mutual legal assistance treaty with the United Kingdom through the State Department. That mechanism had worked for Berman in other investigations.

"But that was not what happened with Prince Andrew," he says.

"We got absolutely nowhere. Were they protecting him? I presume someone was."

The public tensions between prosecutors and Prince Andrew's team intensified in June of 2020 when the prince's lawyers accused Berman of "seeking publicity rather than accepting the assistance proffered".

"Just to be clear: there was no assistance proffered," Berman writes.

"The prince offered to send us some kind of written statement, but that's not how we do investigations. Even for British royals.

Prince Andrew, Virginia Roberts, aged 17, and Ghislaine Maxwell. Prince Andrew always denied sexual relations with Roberts. Photo / File

"Prince Andrew clearly knew Epstein and Maxwell. He was on the island. He was at the mansion in New York. He was in London with them. We had a lot of questions for him, and those questions remained unanswered."

The controversy swirling around Prince Andrew came to the forefront again during the procession for the Queen's coffin in Edinburgh, Scotland this week.

As he and other family members proceeded along the city's Royal Mile, he was heckled by a 22-year-old man wearing a Melbourne City FC football top.

"Andrew, you're a sick man," the bystander yelled.

Police pulled him from the crowd as several other members of the public pushed and hurled abuse at him.

In February, Prince Andrew settled a lawsuit with one of Epstein's victims, Virginia Giuffre, who had accused him of sexually abusing her when she was 17 years old.

The Duke of York strongly denied the claims and has never faced any criminal charges.