Britain's Prince William has settled a phone-hacking claim against Rupert Murdoch's UK newspaper arm for a "huge sum" after a secret deal struck with Buckingham Palace, lawyers for the heir's brother Prince Harry said in court documents.

Harry, the younger son of King Charles, is suing Murdoch's News Group Newspapers (NGN) at the High Court in London for multiple unlawful acts allegedly committed on behalf of its tabloids, the Sun and now defunct News of the World, from the mid-1990s until 2016.

In preliminary hearings this week, NGN, which has paid out millions of pounds to settle more than a thousand phone-hacking cases, is seeking to strike out claims by the prince and British actor Hugh Grant, arguing they should have taken action sooner.

It also denies anyone from the Sun was involved in any unlawful activity.

In a submission to the court, Harry's legal team said the reason he had not brought action before was because a deal had been agreed between NGN and the "institution" - Buckingham Palace - to hold off any claims until the conclusion of other outstanding phone-hacking litigation.

"In responding to this bid by NGN to prevent his claims going to trial, the claimant has had to make public the details of this secret agreement, as well as the fact that his brother, His Royal Highness, Prince William, has recently settled his claim against NGN behind the scenes," his lawyers said.

In a witness statement, Harry said NGN had settled William's claim "for a huge sum of money in 2020... without any of the public being told, and seemingly with some favourable deal in return for him going 'quietly' so to speak".

Prince William's office said it could not comment on ongoing legal proceedings and NGN had no comment.

During a criminal trial brought against News of the World journalists and others in 2014, its former royal editor Clive Goodman said in the mid-2000s he had hacked the voicemails of Harry as well as those of William, and William's wife Kate.

Her phone was hacked 155 times, William's 35 and Harry's nine times, Mr Goodman said.

In his 31-page statement, Harry railed against senior NGN figures and his own family, who he has accused of being in cahoots with the press to protect their image, saying the secret deal was struck to avoid a member of the royal family in the witness box.

Buckingham Palace "wanted to avoid at all costs" the reputational damage caused by publication in the 1990s of details of an "intimate telephone conversation" between Charles and the now Queen Consort Camilla, when his father was still married to his mother Princess Diana, his statement said.

Queen's backing

His grandmother, the late Queen Elizabeth, had in 2017 had given her backing for him to pursue his case and seek an apology from Rupert Murdoch himself, said Harry, who is currently involved in four cases against British newspapers.

But despite the queen's intervention, he said a year later the palace lawyer had told him "nothing could be done as NGN were not in a position to apologise to Her Majesty the Queen and the rest of the Royal Family at that stage".

In his submission, NGN's lawyer Anthony Hudson denied there was any "secret agreement" between the publisher and the royal family. He argued that, even if there was a deal, it did not affect their case that the lawsuit was brought too late.

Harry, who now lives in California, was not in court, but would be watching proceedings by videolink, his lawyer David Sherborne said.

In 2012, Murdoch's British newspaper group issued an unreserved apology for widespread hacking carried out by journalists at the News of the World which the media mogul had shut down amid a backlash.

But it has always rejected any unlawful activity at the Sun which was previously edited by Rebekah Brooks, now chief executive of his British arm, News UK. She has always denied knowledge of phone-hacking and was found not guilty in the 2014 trial of involvement.

Harry said in his statement he was "absolutely astonished" by this. His fury at the treatment of his wife meant he had sought to keep the press away from his glitzy wedding to Meghan in 2018, but his father's office had been unhelpful.

"They had a specific long term strategy to keep the media (including NGN) onside in order to smooth the way for my stepmother (and father) to be accepted by the British public as Queen Consort (and King respectively) when the time came," Harry wrote.

Anything that might "upset the applecart", including phone hacking claims, was to be avoided at all costs, he said.

The case is one of four Harry is pursuing against British newspapers.