We still don't know which specific allegations Thames Valley Police arrested Andrew Mountbatten-Windsor over this morning, with the force only saying that it was on suspicion of misconduct in public office.

However, we know anti-monarchy group Republic reported Andrew to the police over allegations first reported by BBC News.

Earlier this month, we reported on emails released in the US as part of the disclosure of documents linked to the Jeffrey Epstein investigation.

The former prince is alleged to have shared confidential documents with Epstein in 2010, who by that time was a convicted sex offender.

The email dates back to Andrew's time working as a trade envoy on behalf of the UK government.

It allegedly shows he forwarded reports of his visits to Singapore, Hong Kong and Vietnam to Epstein, and confidential details of investment opportunities.

Official terms of reference for the role of trade envoys state it "carries with it a duty of confidentiality in relation to information received".

Andrew has consistently and strenuously denied any wrongdoing. Being named in the Epstein files is not an indication of misconduct.

Today, Andrew Mountbatten-Windsor was arrested and is being held in custody on suspicion of misconduct in public office.

There's been a lot of developments - and there's still a lot we don't know.

BBC Newscast hosts Adam Fleming and Laura Kuenssberg break down the developments with royal correspondent Jonny Dymond and home and legal correspondent Dominic Casciani in the latest episode of Newscast.

You can listen to the episode here.

Jack Fenwick
Political correspondent

We've just had some more detail relating to Andrew Mountbatten-Windsor's arrest this morning.

BBC News understands that Thames Valley Police contacted the Home Office to give them advance warning before Andrew Mountbatten-Windsor was arrested.

Image source, PA Media

If you’re just reading in this evening, Andrew Mountbatten-Windsor was arrested on Thursday morning and is being held in custody on suspicion of misconduct in public office.

Thames Valley Police said it arrested a man in his sixties and is carrying out searches at addresses in Berkshire and Norfolk.

We’ve also heard from the King, who said he received the news of Andrew’s arrest with “the deepest concern”.

“The law must take its course,” he said, adding that the authorities have “our full and wholehearted” co-operation.

We've heard the Prince and Princess of Wales are supporting the King's statement, and Prince Harry's team says they will not be saying anything at this time.

Both the King and Queen have continued with their public engagements, with Charles attending an event in central London.

Andrew has previously denied wrongdoing in relation to Epstein; he has not responded to the BBC’s requests for comment on any of the specific allegations in relation to the release of millions of Epstein files in January.

The King continued with planned engagements throughout Thursday following his brother's arrest.

This afternoon, he was seen attending an event to mark the start of London Fashion Week. He did not make any comments when questioned by reporters upon arrival and departure - but you can read his earlier statement here.

Earlier in the day, he was also photographed greeting officials at St James's Palace, including the ambassadors of El Salvador and Spain, and the High Commissioner for Kenya.

Image source, Reuters

Image source, PA Media

Image source, PA Media

Dominic Casciani
Home and legal correspondent

Andrew Mountbatten-Windsor’s arrest means the police have the right to take a custody picture, his fingerprints and DNA.

If he is going to be held for more than six hours, it must be at a dedicated custody suite.

These are part of what are now commonly known as police investigation centres, dedicated facilities to centralise the holding of all suspects so they can all be interviewed efficiently and looked after properly.

The police cells themselves are basic - the objective is to hold someone securely, safely with decency, not inhumanely. So that means there is bedding, offers of changes of clothing - you will see cell-issued track suits in many clips of interviews released during trials - regular meals, and rules allowing someone to sleep.

As for interviews, the precise timing of those - there can be more than one session - depends on what the police know so far and what they learn in the hours after an arrest.

Each police force area has a duty solicitor scheme - incredibly hard-working criminal defence solicitors who independently advise people on their rights during the shock of the early hours after an arrest.

They often hand over to a specialist solicitor, such as when a suspect has an existing lawyer who is eventually able to get to the interview.

Sam Harrison
Reporting from Buckingham Palace

A short while ago, the King left Buckingham Palace in a large convoy led by police.

Crowds cheered and waved as the convoy went past, with the King visible in one of the cars.

Dominic Casciani
Home and legal correspondent

In England, there are a number of overlapping laws that constrain what the police - and, as a consequence, the media - might be able to say about a live investigation.

If someone is arrested, the law of Contempt of Court is very clear that they have a right to a fair trial - assuming they are going to be charged - and that right should not be damaged by what’s known as prejudicial reporting.

Details of a police investigation, such as precisely what detectives are looking for, why they are looking for it, what they have gathered so far and their assessment of that evidence, is all material that could sway the public’s mind.

That is why the British media often says very little about a live case compared with other countries where there is more of a free for all.

The second is privacy. This is a very hot topic in British media and criminal justice law - but the basic rule is that the police will not, other than in very exceptional circumstances, name someone who is under investigation.

Why? Because investigation is not proof of a crime. People who are suspected of wrongdoing are entitled to get their life back if and when police conclude they were not involved in any wrongdoing.

Image source, Pool/Getty Images

Prior to arresting Andrew Mountbatten-Windsor on suspicion of misconduct in public office, Thames Valley Police had been assessing a complaint submitted by anti-monarchy group Republic over the alleged sharing of confidential material with Jeffrey Epstein.

Thames Valley Police also previously said they were separately assessing allegations that a second woman was sent to the UK by Epstein for a sexual encounter with the former prince.

Several other police forces have said they are assessing whether to launch investigations into matters linked to Epstein. None of the actions of the other police forces relate to today's arrest.

• Essex Police - examining flight logs and emails referencing Epstein's private jet using Stansted Airport
• Bedfordshire Police - assessing Epstein's use of London Luton Airport
• Met Police - launched a criminal investigation into Peter Mandelson, following claims he passed market-sensitive information to Epstein
• Surrey Police - seeking information on an allegation of human trafficking and sexual assault dating back to the mid-1990s
• Norfolk Constabulary - reviewing Epstein files but have not received specific allegations
• Wiltshire Police - reviewing its records and "cannot definitively say that we have not had any allegations at this stage" - said it had supported the Met
• Police Scotland - said it wanted to "speak to anyone with information" about Epstein's private jet using Edinburgh Airport
• West Midlands Police - confirmed it was assessing Epstein's use of Birmingham Airport

Andrew Mountbatten Windsor has denied wrongdoing relating to the Epstein files.

Dominic Casciani
Home and legal correspondent

We don’t know why the police have decided they had to arrest Andrew Mountbatten-Windsor, which happened at around 08:00 this morning.

The law that constrains the police’s power says officers can only hold someone if they have “reasonable grounds” to do so. Those include:

• To conclusively establish their identity and other personal details
• To prevent the suspect harming themselves or others
• To ensure an effective investigation
• To prevent someone from disappearing

Police can initially hold someone for 24 hours and they must be taken to a special custody suite if held for more than six hours.

If detectives need longer, they must apply for more time, first to a superintendent and ultimately to a magistrate.

Arrest comes with rights - including to speak privately to an independent criminal defence lawyer.

Jonny Dymond
BBC royal correspondent

At best, this is a line drawn, a degree of separation. At worst, it is a body blow to the House of Windsor.

Whether there have been trials and cases like this before is unimportant - the times have changed.

And whatever titles and styles may have been stripped from him, this is the King's brother, the late Queen's son.

This was a senior member of the Royal Family whose activities for his country have led to investigation and arrest.

It is hard to think of a much greater challenge for the Palace.

The King closes his message with the words "duty" and "service" - the foundation of the modern monarchy, the mantra of the Royal Family.

The arrest of Mountbatten-Windsor leaves both more vulnerable.

Tim Muffett
Reporting from central London

The King has been attending an event to mark the start of London Fashion Week.

As he arrived he was asked by reporters whether he had any reaction to the arrest of his brother Andrew Mountbatten-Windsor, but he didn’t respond.

A number of well wishers were there to greet him as he made his way inside.

The King was welcomed by the British Fashion Council and toured an exhibition highlighting innovation and sustainability within British fashion – issues he is passionate about.

He also viewed an exhibition by Stella McCartney, a newly appointed ambassador of his Sustainable Markets initiative.

Image source, Neil Mockford/GC Images

The King was met with a mixture of questions about Andrew Mountbatten-Windsor and cheers as he arrived at an event in central London a short while ago.

Like the Queen earlier, the King has decided to go ahead with previously scheduled engagements today despite news of his brother's arrest.

Earlier, he released a statement saying "the law must take its course" - and, as we reported earlier, neither he nor Buckingham Palace were told in advance that the former prince was to be taken into custody this morning.

Lucy Manning
Special correspondent

We now know that at about 08:00 police officers arrived at the Sandringham Estate, where Andrew Mountbatten-Windsor has been staying, to arrest him.

A news agency captured pictures of unmarked police cars arriving and plain clothes officers.

At 09:54, the BBC was the first to confirm that Andrew had been arrested in relation to misconduct in a public office. The news broke on all our platforms moments later.

Shortly after, Thames Valley Police released a statement confirming that a man in his sixties had been arrested and was in custody, and they were carrying out searches at addresses in Norfolk and Berkshire.

The BBC saw uniformed officers at Royal Lodge in Windsor, where Andrew had lived until recently.

The extraordinary morning ended with statement from the King at midday, saying he had learned with “the deepest concern” of Andrew’s arrest and that “the law must take its course".

The King had not been informed in advance that an arrest would take place today.

Listen to the moment we broke the news here:

Daniel Sandford
UK and home affairs correspondent

Typically, an initial arrest in a white collar crime would be for a few hours to allow searches to be conducted and initial questioning to be done.

It is very unlikely that somebody would be held in custody overnight.

Although police can potentially hold someone for 24 hours and get extensions, that really is not very likely.

After that, typically the person who has been arrested is given police bail and a date to return to a police station for potential further questioning.

At some point further down the line - maybe weeks away - there will have to be a decision made by the Crown Prosecution Service and Thames Valley Police about whether to charge him with misconduct in public office.

My guess is it will be weeks before any really substantial decision is made as to whether this is something that needs to be taken further and into the courts.

When a case appears on papers in court it is R v Smith. The 'R' stands for Rex - the King.

If Andrew were to be put on trial, it would be the King versus Andrew Mountbatten-Windsor, his brother.

As we've been reporting, unmarked police arrived at Sandringham Estate in Norfolk this morning, where Andrew Mountbatten-Windsor was arrested at around 08:00.

In recent weeks, the former prince had left Windsor to set up a temporary home in a property on the Sandringham Estate, while his future permanent residence at nearby Marsh Farm is being renovated.

The Sandringham Estate was bought as a private country retreat for the future Edward VII when he was Albert, Prince of Wales, in 1862, and has since been passed down from monarch to monarch.

It remains a country retreat for the Royal Family and is where they traditionally gather at Christmas.

It is understood Andrew is living temporarily at Wood Farm, a secluded property near the village of Wolferton, which his father, the late Duke of Edinburgh, chose as his primary home when he retired from public life in 2017.

Today, Sandringham is a hive of police activity.

Image source, PA Media

Queen Camilla has been asked about Andrew's arrest while at an engagement in central London.

As we reported earlier, the Queen attended a lunchtime concert in Westminster and was greeted by representatives when she got there.

In front of cameras as she headed to her car, the Queen was heard in footage being asked "are you concerned about Andrew's arrest your Majesty". She was seen waving but did not respond to the question.

Image source, PA Media

We can now bring you a little bit more detail about Andrew Mountbatten-Windsor's arrest.

He was arrested at a property on the Sandringham Estate in Norfolk at approximately 08:00 this morning.

That property, as well as his former home at Windsor Great Park, continues to be searched by police.

Andrew remains in custody but we still don't know where the former prince is being held.

Image source, PA Media

Former Prime Minister Gordon Brown has told BBC News he submitted a five-page letter to several UK police forces, including the Metropolitan Police, Sussex Police and Thames Valley Police, providing new and additional information from the Epstein files.

It comes in the wake of the arrest of Andrew Mountbatten-Windsor for misconduct in public office, which the BBC understands is in relation to activity during his time as a trade envoy.

In a statement, Brown says the new information is in addition to what he submitted to the forces last week, in which he "expressed my concern that we secure justice for trafficked girls and women".

Andrew has previously denied any wrongdoing.