Andrew Mountbatten-Windsor is taking legal action against Thames Valley Police and the Central Criminal Court over search warrants used during the investigation that followed his arrest earlier this year.
The former Prince Andrew is seeking a judicial review of the warrants, which authorised searches of properties connected to him in February.
A High Court hearing is due to take place on Thursday as the legal process gets under way.
Here is everything we know so far.
Why is Andrew Mountbatten-Windsor taking legal action?
Mountbatten-Windsor’s lawyers are challenging the lawfulness of search warrants obtained by Thames Valley Police before his arrest.
The warrants were issued by a judge at the Central Criminal Court on 18 February, one day before Mountbatten-Windsor was arrested.
They allowed police to search properties connected to him, including Marsh Farm on the Sandringham estate and Royal Lodge on the Windsor estate.
Mountbatten-Windsor is seeking a judicial review of the actions of Thames Valley Police and the Central Criminal Court in relation to the warrants.
A High Court judge has granted him permission to bring the challenge.
The case does not itself determine whether Mountbatten-Windsor committed any offence. Instead, the court will consider questions surrounding the legality of the warrants.
What happened when police searched the properties?
Police officers carried out searches at properties linked to Mountbatten-Windsor in the days following his arrest.
Officers were seen at Marsh Farm on the Sandringham estate and at Royal Lodge, his former home on the Windsor estate.
The searches formed part of the investigation into alleged misconduct in public office.
Mountbatten-Windsor was arrested on 19 February, his 66th birthday, and taken to Aylsham police station.
He was interviewed under caution before being released under investigation.
He has consistently denied wrongdoing connected to his association with Jeffrey Epstein.
What is the investigation about?
The police investigation concerns suspected misconduct in public office.
The inquiry followed the publication of material from the Epstein files in the United States.
Among the material were emails appearing to show Mountbatten-Windsor sharing official information with Jeffrey Epstein and others during the period when he served as the UK’s trade envoy.
Thames Valley Police has previously said that allegations of sexual misconduct could also be considered as part of its investigation.
Misconduct in public office is a broad common-law offence which can cover a range of alleged behaviour, including the improper disclosure of confidential information, corruption, dishonesty, wilful neglect of duty and certain forms of sexual misconduct.
The existence of an investigation or arrest does not mean that an offence has been proved.
What is happening in court?
A High Court hearing is scheduled for Thursday.
The hearing is initially expected to take place in private.
Mr Justice Hilliard will first consider an application concerning whether certain documents connected to Mountbatten-Windsor’s judicial review challenge should be kept private.
Thames Valley Police and the Central Criminal Court are opposing the challenge.
The Central Criminal Court, commonly known as the Old Bailey, was the court whose judge issued the warrants.
The proceedings therefore concern the legal basis on which the warrants were obtained and issued.
What does Andrew want the court to do?
Mountbatten-Windsor wants the search warrants to be quashed.
His lawyers are effectively asking the court to examine whether the warrants were lawfully issued.
However, even if the challenge succeeds, that would not necessarily mean that everything obtained during the searches would automatically have to be returned.
Nick Vamos, a criminal lawyer and former head of special crime at the Crown Prosecution Service, told the BBC that challenges over warrants were not unusual.
He explained that, depending on the circumstances, police could potentially apply to the Crown Court to retain material if they had grounds to seize it again.
A more fundamental problem with the granting of the warrants could therefore be required before material obtained during the searches necessarily had to be returned.
Is this a challenge to the criminal investigation itself?
Not directly.
The legal action is focused on the search warrants and the legality of the process surrounding them.
Thames Valley Police’s wider investigation into suspected misconduct in public office is continuing.
The force has previously said it has been working with the United States Department of Justice to obtain further information potentially relevant to its investigation.
A successful challenge to the warrants would therefore not automatically bring the police investigation to an end.
How has Thames Valley Police responded?
Thames Valley Police has confirmed that legal proceedings are under way.
A spokesperson said: “While our investigation into misconduct in public office continues, we are engaged in legal proceedings in relation to warrants previously obtained from the central criminal court. As these legal proceedings are currently ongoing, it would be inappropriate for us to comment further.”
The force has not commented on the specific grounds of Mountbatten-Windsor’s legal challenge.
Why is the case significant?
The challenge represents a significant legal development following Mountbatten-Windsor’s arrest and the searches of properties connected to him.
The Guardian and Daily Telegraph have reported that the case could be the first time in centuries that a member of the Royal Family has challenged the lawfulness of criminal proceedings against them, with the Telegraph drawing a comparison with the trial of Charles I in 1649.
The circumstances are, however, very different.
Mountbatten-Windsor is challenging the legality of search warrants issued as part of an ongoing police investigation. The proceedings are not a criminal trial.
The case also comes after a dramatic fall in Mountbatten-Windsor’s public position.
He was stripped of his remaining royal titles and his Dukedom of York by the King last year following continued scrutiny of his association with Epstein.
He has subsequently lost his former public role and has faced increasing distance from organisations and charities with which he was previously associated.
Could this affect the police investigation?
Potentially, but the consequences will depend on the outcome of the legal challenge.
If the court finds that the warrants were unlawful, there could be further legal arguments over material obtained during the searches and whether it can continue to be used.
However, a successful challenge would not necessarily mean the police have to abandon their investigation.
The legal proceedings could therefore become an important part of the wider case without determining the ultimate outcome of the investigation itself.
What happens next?
The immediate next step is the High Court hearing on Thursday.
The judge is initially expected to consider whether documents relating to the judicial review proceedings should remain private.
The substantive challenge to the warrants will then proceed through the courts.
Meanwhile, Thames Valley Police says its investigation into suspected misconduct in public office remains ongoing.
For now, Mountbatten-Windsor remains under investigation following his arrest in February.
No criminal charge has been brought against him in relation to the investigation, and he continues to deny wrongdoing linked to his association with Epstein.
The High Court proceedings are therefore likely to provide the next significant development in a case that has already dramatically changed Mountbatten-Windsor’s public position.
