The publisher of the British tabloid The Mirror, accused by Prince Harry and other celebrities of unlawful information gathering, apologised at the opening of a trial in London on Wednesday.

The younger son of King Charles III has been involved in several legal cases against British newspaper publishers since moving to California and stepping down from royal duties in early 2020.

Harry is one of several high-profile claimants bringing damages against Mirror Group Newspapers (MGN) over allegations of unlawful information gathering, including phone hacking.

The group publishes titles including The Mirror, the Sunday Mirror and Sunday People.

The trial at the High Court in London is expected to last up to seven weeks with Harry set to take the stand in June.

At the start of the trial on Wednesday, the publisher admitted "some evidence" of unlawful information gathering and assured that "such conduct will never be repeated".

The group admitted that a private investigator was instructed by a journalist at The People to unlawfully gather information about Harry's activities at a London nightclub one night in 2004.

It apologised to Harry "unreservedly" and said he was entitled to "appropriate compensation" without providing further details.

But MGN lawyer Andrew Green said voicemail interception was denied. He also argued that some of the claims were brought too late with some of the stories in question dating back more than twenty years.

'Flood of illegality'

Lawyer David Sherborne, representing Harry and other claimants, submitted that the use of unlawful information-gathering by journalists from the titles of MGN was happening "at an industrial scale".

"It was a flood of illegality," Sherborne told the hearing, adding that "this flood was being authorised and approved of by senior executives".

Harry, 38, has had a difficult relationship with the media, particularly since he and his American wife Meghan left the royal family in early 2020.

He is also pursuing claims against two other media companies, the publisher of The Sun and, separately, the publisher of the Daily Mail. Those cases will be decided later this year.

Harry holds the media responsible for the death of his mother Princess Diana, who was killed in a car crash in Paris in 1997 after being pursued by paparazzi photographers.

His tell-all best-selling memoir "Spare" broke publishing records when it came out earlier this year.

Harry attended last weekend's coronation without Meghan, who remained in California with the couple's two children, and was not given a formal role in the ceremony.

He was absent from the royal procession through central London after the ceremony and did not join other members of the royal family on the Buckingham Palace balcony.