Leading tabloid newspapers concealed or destroyed evidence that they illegally targeted Prince Harry and his circle of friends and advisers over many years, according to allegations contained in his unprecedented legal action against two media groups.

He is joining scores of other people in a group claim that alleges editors and executives at Mirror Group Newspapers, publisher of the Daily Mirror, and News Group Newspapers (NGN), publisher of the Sun and the defunct News of the World, mounted an industrial-scale cover-up over more than 20 years.

The Byline Investigates website, which first reported the Duke of Sussex was taking legal action, says the group claim is due to be heard next October. The Observer understands the claims made by each group member carry around five pages of allegations relating to hacking and blagging – obtaining personal information illegally – and around 20 pages outlining allegations of concealment and destruction of evidence. The claims cover 1994 to 2011.

Byline reports the duke’s claim could see his lawyers seek to establish whether the newspapers intercepted voicemails of his late mother, Diana, Princess of Wales. The website claims it will also explore whether, even after Diana’s death in August 1997, private investigators were hired to illegally target her friends and family.

Legal experts have suggested the duke would have a problem bringing the claim. Under the Limitation Act, there is a six-year window from when a claimant becomes aware of the privacy breach to bring a claim.

Clive Goodman, a News of the World journalist, and Glenn Mulcaire, a private investigator, were jailed in 2007 for offences including the hacking of voicemails of aides working for the duke and his brother, Prince William.

However, it is clear that the duke’s claim extends at least a decade beyond that 2007 case. As with the other group claims, the duke alleges evidence was destroyed and concealed and so any limitation defence would fail under Section 32 of the Act if it were shown to have concealed wrongdoing.

Clive Goodman, royal correspondent of News of the World, leaves the Old Bailey in 2006. Photograph: Toby Melville/Reuters

“This is far more serious than just phone-hacking because these allegations involve perverting the course of justice, perjury and fraud against senior executives and senior editors,” a source familiar with the claim explained. This would shift the focus away from the actions of individual journalists to the higher echelons of the newspaper organisations.

Hitherto the focus of many claims has been on the role of Mulcaire. “Mulcaire is just one tiny part of this,” the source said. It is understood that the claim has resulted in the disclosure of thousands of alleged payments to private investigators by Mirror Group and tens of thousands by the Sun and News of the World.

There is speculation that close friends and former girlfriends of the duke may have been hacked. “The royal family might have tight procedures for guarding their privacy, but the duke’s nightclub-going friends may not,” the source suggested.

The duke’s lawyers will attempt to obtain evidence of what, if any, personal information was obtained by the newspapers. This could include school reports, financial statements and health records. The sweep could extend back to include his mother.

If the case were to go to court, it would raise the prospect of the duke appearing in the witness box. Many executives and senior editors – including Rebekah Brooks, the chief executive of News UK, the parent company of NGN, and Piers Morgan, former editor of the Mirror – would come under further scrutiny. Both have denied under oath knowing of any wrongdoing on their watch.

In 2015, the Crown Prosecution Service said there was “no evidence” NGN had deleted emails to pervert the course of justice. Both News UK and Reach UK, owner of the Mirror, declined to comment.

The duke’s claim against the two news groups comes after his wife, the Duchess of Sussex, launched a legal case against the Mail on Sunday. She claims the paper breached her privacy and copyright by publishing a private letter to her father. The paper has said it will vigorously defend the claim.

Richard Palmer, the Daily Express royal correspondent, said: “I know I am not the only reporter to have received death threats from ‘fans’ who have accused just about every British journalist who covers the royals of racism. I worry that his wild, unjustified statement will place us in further danger. Unlike him, we don’t have police protecting us. He will have blood on his hands if any of us is harmed.

“He and Meghan will always be a story and have the potential to do great things for our country. Indeed they have helped the monarchy reach parts of our society that never felt touched by the royal family.”

The timing of the Sussex’s legal actions has invited speculation that they were coordinated. However, it is understood the duke’s action followed weeks of pre-action correspondence.

Writing in the Observer, Princess Diana’s former private secretary, Patrick Jephson, warns her son’s approach could backfire. “Public sympathy will start in the duke’s corner but is notoriously volatile,” he says.