Harry, King Charles' younger son, and more than 100 others including celebrities and high-profile figures, are suing Mirror Group Newspapers (MGN), the publisher of the Daily Mirror, Sunday Mirror and Sunday People, at the High Court in London.

They allege the papers habitually accessed private information by phone-hacking, deception and other illicit means between 1991 and 2011, and that editors and senior executives approved of the actions.

"MGN strongly denies these allegations," said Andrew Green, the lawyer representing the publisher, now owned by Reach.

In 2015, the High Court ordered MGN to pay out large sums to eight claimants after it admitted stories about them had been obtained by phone-hacking, a ruling which Green said the publisher fully accepted and made "painful reading".

Since then, he said, the company had settled more than 600 claims at a cost of over 100 million pounds in damages and costs. But the claims put forward by Harry and three others which form test cases for the current trial were in evidential terms far from those which it had originally settled, he said.

Evidence of call data to back up their phone-hacking allegations was "slim to utterly non-existent", and a large proportion of stories involved were of a "breathtaking level of triviality", many of which the claimants had not read at the time.

There was "nothing to show widespread voicemail interception" beyond that already admitted, Green added.

He said those making allegations of dishonesty about MGN's board members, accusing them of misleading parliament and a public inquiry into press behaviour, "should be held to the highest standards" of proof.

"It doesn't seem to us those are allegations that can be properly made," he said.

Where there was evidence MGN journalists had instructed private investigators to act unlawfully, the publisher had made admissions, he said.

Court documents released on Wednesday showed MGN had apologised to Harry for unlawfully seeking information about him and that he was entitled to compensation.

The trial, due to last some seven weeks, is initially focusing on generic allegations before later turning to the specific claims of Harry and the three other test cases.

The claimants' lawyer, David Sherborne, has sought to demonstrate that unlawful activity was widespread through invoice payments made to private investigators and details of their phone calls to journalists.

"This was a cover-up, plain and simple," he told the court as he concluded his opening statement.

(Reporting by Michael Holden; Editing by Nick Macfie)

By Michael Holden