By Michael Holden and Sam Tobin

LONDON, Jan 21 (Reuters) - Prince Harry's legal battle against Rupert Murdoch's British newspaper group goes to trial at the High Court in London on Tuesday with the royal seeking a ruling that senior figures knew about and covered up widespread wrongdoing.

Harry, along with former senior lawmaker Tom Watson, 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.

The prince says his mission is not money but to get to the truth, after other claimants 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.

"One of the main reasons for seeing this through is accountability, because I'm the last person that can actually achieve that," Harry, who is set to appear as a witness himself in February, said last month.

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 more than 1,300 lawsuits involving celebrities, politicians, well-known sports figures and ordinary people who were connected to them or major events.

Harry's legal team has said in earlier court documents that his older brother Prince William, the heir to the throne, had settled his own case against NGN in 2020 for "a very large sum of money".

While Murdoch closed the News of the World in 2011, the publisher has always rejected claims there was any unlawful activity at the Sun and says it will fully defend the claims.

The eight-week trial will at first consider "generic issues" such as the extent of any phone-hacking and unlawful information gathering at the papers.

Harry's team will argue that senior executives and editors knew unlawful behaviour was widespread, and allege that they misled police, provided false statements to a public inquiry into media ethics held from 2011-12 and instigated a massive cover-up with the deletion of millions of emails.

"This allegation is wrong, unsustainable, and is strongly denied," a spokesperson for NGN said. "NGN will be calling a number of witnesses including technologists, lawyers and senior staff to defeat the claim."

As well as Harry, witnesses that are due to be called, or who have provided evidence for the claimants include former Prime Minister Gordon Brown, actors Hugh Grant and Sienna Miller, singer Lily Allen and Heather Mills, the former wife of Paul McCartney.

(Reporting by Michael Holden, Editing by William Maclean)

((michael.holden@thomsonreuters.com;))