Mirror Group Newspapers (MGN) said it would never be repeated.

Lawyers representing Harry told the court he was subjected to the "most intrusive methods of obtaining personal information".

Harry is one of several high-profile figures bringing claims against MGN.

Lawyers argue that executives at the company knew about widespread phone hacking but failed to act.

In a written submission, MGN - which also publishes the Sunday Mirror and Sunday People - said it "unreservedly apologizes" for instances of unlawful information gathering against Harry and others and said that the legal challenge brought by the prince "warrants compensation".

But Andrew Green KC, representing the publisher, added that the publisher denied allegations of voicemail interception in the cases being examined during the trial.

The barrister also said some of the challenges it faces have been brought beyond a legal time limit.

A previous hearing was told Harry's case is that 148 articles published between 1996 and 2010 included information that was allegedly obtained through methods including phone hacking.

Prince Harry is expected to give evidence in June -- the first time a senior royal will be a witness in court in modern times -- with the High Court hearing set to last six or seven weeks.

The estate of the late singer George Michael and actor Ricky Tomlinson have also brought claims against MGN, with "test cases" -- including Harry's -- selected to go to trial from the wider group of claimants.

The other "representative" cases set for trial are that of former Coronation Street actress Nikki Sanderson, comedian Paul Whitehouse's ex-wife Fiona Wightman and actor Michael Turner.

MGN has previously settled a number of claims against it in relation to stories obtained through unlawful means.

It was also involved in a 2015 trial, the only to take place during the long-running litigation, which saw claims brought by ex-footballer Paul Gascoigne, actress Sadie Frost, and Coronation Street actress Shobna Gulati.

Last month, lawyers for the group said that all the witnesses on their side would give evidence in person, paving the way for Prince Harry to take the stand.

He has become an outspoken critic of the tabloid press and has already appeared in court once this year to listen to legal arguments in another case he is involved in.

Harry is party to actions linked to alleged phone hacking against two other companies — the publisher of the Daily Mail, and the publisher of the Sun, both of which deny wrongdoing.

He is bringing a separate libel claim against the Mail's publisher, Associated Newspapers Limited, over an article about his security arrangements with the Home Office.