Public figures such as Doreen Lawrence and Elton John were “induced” to sue the Daily Mail’s publisher on the basis of a private investigator’s now disowned claims of illegal activity, the high court has heard.

Seven people including Prince Harry have accused Associated Newspapers Ltd (ANL) of using unlawful information gathering to obtain stories. John’s partner, David Furnish, and the actor Liz Hurley are also among the group. ANL denies all the claims.

The most serious allegations came from Gavin Burrows, a private investigator who has since said a witness statement containing claims of phone hacking, tapping and bugging was forged.

In written closing submissions in the 10-week trial, ANL’s legal team said the Burrows statement – and other disputed claims made by him – were used to recruit prominent figures to the case.

“It seems that it took time to build the group, and that at least some of the claimants were induced to join and maintain the proceedings on being persuaded … that the grave allegations attributed to Mr Burrows were truthful,” said Antony White, the lead barrister for the publisher.

He said that given Burrows now denied doing anything illegal for ANL, “the most serious of the claimants’ allegations, and the basis upon which Ms Hurley, Sir Elton John and Mr Furnish, the Duke of Sussex and Baroness Lawrence had been persuaded by the claimants’ legal representatives and research team to join the group claim, have effectively fallen away.”

White said it was a “particular tragedy” that Lawrence, 73, had been persuaded to join the case after the Daily Mail’s long campaign for justice for her son Stephen, who was murdered in 1993 in a racist attack.

White said Lawrence had been regarded as a “trophy claimant so prized by the claimants’ lawyers and research team”. He said she had been persuaded to join the case “on the basis of ‘evidence’ that had no substance and ultimately was not even deployed”.

Burrows previously told the court that Lawrence had been “conned” by researchers now working for the claimants’ legal team.

David Sherborne, the lead barrister for the claimants, has said Burrows only made his forgery claims after a huge falling out with Graham Johnson, a researcher for the claimants’ legal team.

In court, Sherborne said Burrows’ subsequent claims that his admissions and testimony were forged were “hopeless” and “frankly risible”.

Earlier in the case, Sherborne said Burrows was just “the original whistleblower” and there was “plenty of hard evidence of Associated using numerous other private investigators to carry out unlawful information gathering”.

White said claims against ANL of unlawful information gathering had been long in the planning by the campaign group Hacked Off. He said it was part of the group’s “political campaign” to show that the publisher had misled the Leveson inquiry into the practices of the press.

At the inquiry, ANL executives said there had been no hacking and that the use of private investigators had stopped in 2007.

White said researchers targeted “national treasures” who might gain public sympathy. He said “headline-grabbing allegations” of tapping, bugging and hacking made at the start of the legal action “generated, as must have been intended, enormous publicity”.

“This robust and comprehensive defence mounted by Associated has resulted in the most serious of the claimants’ allegations being struck out, or falling away, or being abandoned, or significantly reduced, before or during the trial,” he said.

He said there were no documents to support the disputed Burrows confessions.

White said that either ANL had not used private investigators in relation to the articles cited in the case, or that they had been used legally to obtain telephone numbers and addresses. He said a parade of current and former Mail journalists had recounted “a pattern of legitimate sourcing” for stories.

The claimants’ legal team have also focused on claims of alleged “blagging”, including of detailed medical information about the actor Sadie Frost and flight information about one of Prince Harry’s former girlfriends.

The case continues.