Sir Keir Starmer has said "nobody is above the law" when asked about Andrew Mountbatten-Windsor, but declined to say whether the former prince should volunteer himself to UK police.

Speaking before news of Andrew's arrest, the prime minister told BBC Breakfast the principle was "very important" and "has to apply in this case in the same way it would in any other case".

Police are considering allegations including that a woman was trafficked to the UK by the late sex offender Jeffrey Epstein for the former prince. Andrew has consistently and strenuously denied any wrongdoing.

The accusation emerged following the release in the US of documents relating to a trafficking investigation into Epstein.

Asked whether he thought Andrew should voluntarily speak to UK police, Sir Keir said: "I think that's a matter for the police.

"They will conduct their own investigations, but one of the core principles in our system is that everybody is equal under the law and nobody is above the law."

He added: "It's a very important principle of our country... and it has to apply in this case in the same way it would in any other case."

The prime minister said that if MPs in Parliament wanted a debate on Andrew's links to Epstein, he "wouldn't stand in the way".

Thames Valley Police arrested Andrew on Thursday morning on suspicion of misconduct in public office, taking him into custody.

The force is also currently assessing allegations, first reported by the BBC, that a second woman was sent to the UK by Epstein for a sexual encounter with Andrew.

The encounter allegedly occurred at the former prince's residence, Royal Lodge, in 2010. The woman, who is not British, was in her 20s at the time.

The woman's lawyer, Brad Edwards, said that after spending the night with Andrew, the woman alleges she was given tea and a tour of Buckingham Palace.

Millions of files released last month by the US Department of Justice shed new light on Andrew's close relationship with the disgraced financier.

The latest tranche included pictures of him kneeling on all fours over a woman lying on the ground, both fully dressed, while other files repeatedly reference him.

They also appear to show the former prince forwarded sensitive government documents and commercial information to Epstein.

In his interview with Breakfast on Thursday morning, Sir Keir reiterated previous comments he had made suggesting Andrew should testify before the US Congress.

"Anybody who has any information should testify. So, whether it's Andrew or anybody else, anybody who's got relevant information should come forward to whatever the relevant body is," he said.

Following the release of photos and further email correspondence between Andrew and Epstein, the former prince moved out of his home in Windsor to the Sandringham Estate in Norfolk.

A number of exchanges between Epstein and Andrew revealed they were still in touch in the years after the US billionaire pleaded guilty to soliciting a minor.

Epstein died in a New York prison cell in 2019 while awaiting trial on sex trafficking charges.

Nine police forces across the UK have confirmed they are assessing whether to launch investigations into Epstein-related allegations.

In particular, the Metropolitan Police said it was carrying out "initial inquiries" into allegations relating to close protection officers formerly assigned to Andrew.

A former senior Met protection officer told LBC members of the Royalty and Specialist Protection (RaSP) might have "wilfully turned a blind eye" when visiting Epstein's private island.

The Met said in a statement that it had "not identified any wrongdoing" but "initial enquiries into these specific allegations have begun so we can establish the facts".

The force has launched a criminal investigation into former US ambassador Lord Peter Mandelson after documents in the Epstein files suggested he had passed market-sensitive government information to Epstein when he was business secretary in 2009.

On Thursday, Sir Keir reiterated an apology to Epstein's victims for appointing Lord Mandelson as ambassador. Lord Mandelson was sacked in September after new information about the depth of his relationship with Epstein emerged.

"I wanted to apologise to the victims first and foremost for having accepted his lies" about their relationship, Sir Keir said, "and I do so again now."

He added: "I reflected good and hard on that, and as I said to my Parliamentary Labour Party, nobody has been harder on me in relation to that than I have."

Pressure has been growing on Andrew to testify in the US about his links to financier Epstein. Last week, US officials and the family of his prominent accuser, the late Virginia Giuffre, called on him to testify.

In 2014, Virginia Giuffre alleged that as a 17-year-old she had been trafficked by Epstein and his girlfriend Ghislaine Maxwell, and forced to have sex with Andrew - a claim he denies.

Virginia Giuffre filed a civil lawsuit in the US against him in 2021, settling the case in February 2022 for an estimated £12m. She took her own life last year.