The former prince, Andrew Mountbatten-Windsor, is currently in police custody following an arrest early on the morning of his 66th birthday.
Mr Mountbatten-Windsor is under investigation on suspicion of misconduct in public office.
He has always denied any wrongdoing.
The inquiries are believed to relate to his time as UK trade envoy.
Six unmarked police cars and eight plain clothes officers arrived at Wood Farm on the Sandringham estate just after 8am on February 19. It was later confirmed that a man in his sixties had been arrested.
Searches are ongoing at properties in Norfolk and Berkshire.
Andrew Mountbatten-Windsor lived at Royal Lodge on the Windsor estate in Berkshire until January when he moved to Wood Farm on the Sandringham estate in Norfolk.
Nine forces have confirmed in recent days that they are looking into allegations around Mr Mountbatten Windsor.
There has been no comment from Buckingham Palace.
