Watch: What does the ruling mean for the investigation into the former prince?
The High Court has heard that search warrants used by Thames Valley Police to search Andrew Mountbatten-Windsor's homes earlier this year were unlawful.
The force has said it accepted that the 'initial court's decision to issue warrants under the specific piece of legislation used was incorrect', before they searched the former prince's properties on 19 February.
Mountbatten-Windsor was arrested by Thames Valley Police on suspicion of misconduct in public.
He denies any wrongdoing. Special correspondent Lucy Manning is outside the High Court has and explains what we know about the ruling.
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