LONDON — Police who searched the properties of the former Prince Andrew and seized his property in the investigation into his links to the late sex offender Jeffrey Epstein have agreed the search warrants were unlawful, a London judge said Thursday.

Justice Nicholas Hilliard said that the Thames Valley Police had made a significant error in applying for the warrant when they searched the properties of the former prince now known as Andrew Mountbatten-Windsor.

Mountbatten-Windsor was arrested on Feb. 19, on suspicion of misconduct in public office and police searched two of his homes. His lawyers asked the High Court judge to invalidate the warrants under which those searches were conducted.

Hilliard said the parties had agreed to invalidate the warrants before the hearing Thursday.

Mountbatten-Windsor was not in court for the hearing.

Stephens, of the Howard Kennedy firm in London, described the hearing as a preliminary skirmish in the broader legal battle.

“It’s the first step of Prince Andrew and his lawyers saying, ‘Actually, this is tainted evidence. It was obtained inappropriately,’’’ Stephens said. “Therefore it should be excluded from any criminal trial.”

King Charles III stripped Mountbatten-Windsor of his princely title last year as he sought to shield the rest of the royal family from the continuing fallout from his younger brother’s links to Epstein.

While Mountbatten-Windsor, 66, continues to receive a stipend from the king’s private funds, Buckingham Palace has made it clear that those funds may not be used to fund his effort to challenge the search warrants.

The police investigation initially focused on allegations that Mountbatten-Windsor shared sensitive information with Epstein when the former prince was a U.K. trade envoy, but police later said they could also consider other matters.

Police questioned Mountbatten-Windsor for 11 hours before releasing him under investigation, meaning he was neither charged nor exonerated.

It was the first time in nearly four centuries that a senior British royal was placed under arrest.

The allegations against Mountbatten-Windsor came to light when the U.S. Justice Department released millions of pages of documents from its investigation into sex trafficking by Epstein and his connections to a network of wealthy, powerful men around the world.

Mountbatten-Windsor’s ties to Epstein have been a source of embarrassment to the royal family for more than a decade.

Lawmakers questioned the relationship as far back as 2011, when the then-prince was forced to give up his globetrotting role as the U.K.’s special trade envoy. Eight years later, he failed to explain his continuing ties to Epstein in a disastrous interview with the BBC, ending his career as a working member of the royal family.