By Michael Holden and Sam Tobin

LONDON (Reuters) - Prince Harry's lawsuit against Rupert Murdoch's British newspaper group officially begins at the High Court in London on Tuesday, with King Charles' younger son set to appear as a witness himself at the trial next month.

Harry is suing News Group Newspapers over alleged unlawful activities carried out by journalists and private investigators working for its papers, the Sun and the defunct News of the World, from 1996 until 2011.

Harry has said he wants to get to the truth, after about 40 other claimants, including actor Hugh Grant, settled cases to avoid the risk of a multi-million pound legal bill that could be imposed even if they won in court but had rejected NGN's offer.

"They have settled because they've had to settle," he told the New York Times Dealbook Summit last month. "One of the main reasons for seeing this through is accountability because I'm the last person that can actually achieve that."

The NGN case is the latest lawsuit in Harry's war with the British press which began shortly after his marriage to his American wife Meghan in 2018.

Harry and Meghan stepped down from royal duties in March 2020 and moved to California, where they now live with their two children, a decision the prince says was largely due to intrusion, harassment and incitement to hatred from the tabloids.

Critics say he is seeking vengeance on papers for their coverage about him and his barbed comments against other members of the royal family after he used documentaries, his memoir and interviews to criticise editors and senior executives.

The eight-week trial will at first consider "generic issues" such as phone hacking and unlawful information gathering at the papers, whether senior NGN figures knew about it, and whether incriminating evidence had been deliberately destroyed.

It will also examine allegations NGN misled police and provided false statements to a public inquiry into media ethics held from 2011-12.

Specific evidence relating to Harry and another claimant, Tom Watson, a former Labour Party deputy leader, will then be scrutinised, with the prince himself expected to give evidence for at least two days, while former prime minister Gordon Brown is also expected to appear as a witness.

"His claim will be fully defended, including on the grounds that it is brought out of time," a spokesperson for NGN said of Harry's lawsuit.

The spokesperson said Watson had never been a target of hacking, and the allegation that emails had been unlawfully destroyed was "wrong, unsustainable, and is strongly denied".

PHONE HACKING

The fifth-in-line to the throne has already successfully sued Mirror Group Newspapers for hacking voicemail messages on his phone and for other unlawful invasions of privacy, winning substantial damages.

That case saw him become the first senior British royal for 130 years to appear as a witness in court when he provided testimony over two days in June 2023.

There is potentially more at stake for Murdoch's newspaper group. In 2011 it issued an unreserved apology for widespread phone hacking carried out by journalists at the News of the World which Murdoch shut down.

Since then NGN has paid out hundreds of millions of pounds to victims of phone hacking and other unlawful information gathering by the News of the World, and settled claims brought by more than 1,300 people.

But it has always denied any unlawful activity at the Sun, and the upcoming trial will be the first to examine specific allegations against the paper which was previously edited by Rebekah Brooks, now head of News Corp's British arm.

She was found not guilty in 2014 of phone hacking following a criminal trial, and NGN's lawyers have accused Harry's legal team and others of trying to turn the lawsuit into a re-run of old cases and the public inquiry.

The judge previously ruled that Harry could not bring allegations against Murdoch himself. Brooks will not be giving evidence but other current and former NGN staff will be appearing.

(Reporting by Michael Holden; Editing by Alison Williams)