Lawyers representing alleged victims of convicted sex offender Jeffrey Epstein have threatened to subpoena Prince Andrew, meaning he has to give evidence or documents to a United States court.

The BBC revealed pre-trial witness subpoenas have been prepared for five cases involving alleged victims of Epstein.

These subpoenas could be served to Prince Andrew … if he returns to the US.

Why are we talking about subpoenas?

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A subpoena is a request for evidence or documents, and requires a person to comply with the court order.

Civil rights lawyer Lisa Bloom, who is representing five of Epstein's alleged victims, told The Times if Prince Andrew won't testify voluntarily, she is ready to get a court order, a subpoena, requiring him to give evidence.

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"I hope we don't have to subpoena him," she said.

"We certainly could … if we determine that he has relevant information to our cases."

According to the office of the Law Revision Counsel's US Code, a subpoena can be issued to a person within the United States, or United States national or resident who is in a foreign country.

Subpoenas would have to be enforced by a judge and signed off once the Prince was on US soil, and he could challenge them in court if he did not want to give evidence.

But what if Prince Andrew doesn't return?

In the case of Prince Andrew, if he stays in the UK he doesn't fall under United States jurisdiction, so the process becomes a little more complicated.

Professor of International Law at the Australian National University Donald Rothwell said one avenue US law enforcement could take is through a mutual legal assistance treaty that exists between them and the UK.

"Mutual legal assistance is really designed to assist with aspects of precisely the matter that we're talking about, the way in which you would seek to get evidence given by someone in the UK in terms of court proceedings in the United States," Professor Rothwell said.

Prince Andrew shared his side of the story in a "car crash" BBC interview last month, but he has not told his version of events under oath. ( News Video )

"These treaties are designed to facilitate these processes, and I emphasise 'facilitate', because depending on the type of request that's being made, there are limits in terms of how a mutual legal assistance treaty will be able to assist one country in terms of legal proceedings in another.

"It should be said that there are other processes that can also be put into play, but this is a more formal and most effective legal process that allows for these types of matters to be facilitated."

Is using the treaty a rare thing?

According to Professor Rothwell, not really.

He said the processes were fairly well-established, particularly in countries with advanced legal systems like Australia, which has mutual assistance treaties with a number of countries.

US lawyers have threatened to subpoena Prince Andrew, calling for him to give evidence on his association with Jeffrey Epstein. ( Reuters: Toby Melville )

"In the case of the UK and the US, where there's a significant movement of people on business and travel on a daily basis, getting up to all sorts of legal issues in either country, it really isn't that exceptional," he said.

"The only thing exceptional about this case is that it involves a member of the British Royal family. Obviously from the media's perspective, there's significant interest and I understand that.

"To a degree, this is relatively bread-and-butter other than the particular dimensions of the individual whose evidence is being sought. Not only the high media profile and media interest and public interest in the matter, but also the possible legal sensitivity that throws up for the United Kingdom Government in terms of the way in which they would seek to respond to any formal request from the United States to facilitate a subpoena request in the UK."

One of Jeffrey Epstein's alleged victims, Virginia Roberts Giuffre, spoke to media outside a Manhattan court in August after Epstein's death. ( AP: Bebeto Matthews )

Wait, what's the catch?

Professor Rothwell said while the treaty could certainly address a request from the US for Prince Andrew to respond to a subpoena, the specific treaty in place between the US and the UK had an interesting clause that could potentially come into play.

Article 3 in the treaty outlines that the "requested party" (in this case, the UK) may refuse assistance if "the Requested Party is of the opinion that the request, if granted, would impair its sovereignty, security, or other essential interests or would be contrary to important public policy".

"You can understand how a UK government could take the view that it would not be appropriate for it to facilitate the serving of a subpoena on the Queen's son," Professor Rothwell said.

"So, whilst Andrew doesn't enjoy diplomatic immunity and he doesn't enjoy what international lawyers call 'head of state immunity', there is this interesting provision which a UK government could take the view that it's not appropriate for it to facilitate the serving of a subpoena on Andrew in the United Kingdom."

There's no evidence at this stage to say that the UK Government has refused to assist the US in serving a subpoena to Prince Andrew, and he has made a public statement saying he was "willing to help any appropriate law enforcement agency with their investigations".

Prince Andrew pictured with other royals and British Prime Minister Boris Johnson in early November 2019. ( Reuters: Chris Jackson )

Professor Rothwell said it was important not to confuse mutual legal assistance with extradition.

"Extradition is the process that gets perhaps more prominence, and it's a similar type of legal process, but of course extradition physically requests the return of an alleged offender from one country to another," he said.

"In the case of the US and the UK, that's the process that Julian Assange is going through at the moment."

Can Prince Andrew ever go back to the US?

Well, yes. Prince Andrew could potentially save a whole lot of international back-and-forth by volunteering to speak under oath before a United States court.

Professor Rothwell said it would simplify some matters if Prince Andrew was to voluntarily assist the US courts by agreeing to give evidence, but he could find himself subject to other lawsuits when he arrives.

Prince Andrew told the BBC he would testify under oath about his connections with Epstein. ( Reuters: Neil Hall )

"Importantly, because Andrew is not a diplomat, and because he doesn't enjoy sovereign immunity because he's not the sovereign, he can't plead immunity before the US courts," Professor Rothwell said.

"From a legal perspective, I think it would not be very prudent for him to return to the United States at the moment while all of this is going on. Certainly if voluntarily he was to agree to give evidence on certain terms and conditions that he might set while he's in the UK, that's a good outcome from his perspective and it obviously assists the US legal proceedings."

Professor Rothwell said Prince Andrew volunteering to give evidence from the UK on his terms was a likely scenario.

Prince Andrew pictured with Virginia Roberts, who alleges she was forced to have sex with the prince three times as a teen. ( Supplied )

"The last thing that Andrew and the last thing that the Royal Family wants is for him to become embroiled in US legal proceedings," he said.

"I think the last thing that Buckingham Palace would want is for the UK Government to be forced to look carefully at the terms of the mutual assistance treaty, and the terms of the treaty which could see the UK Government quite legitimately say 'no, we're not going to assist the US'.

"For a whole series of reasons, I think that would be the best outcome for everyone including Andrew.

"And obviously, that those persons who feel aggrieved about the whole matter in terms of Epstein in the United States feel that they've received appropriate support and assistance in terms of their ongoing legal proceedings in the US."