The amount of lost or destroyed documents relating to the Daily Mail publisher’s use of private investigators is “stark in the extreme”, the high court has heard.

However, the thin surviving evidence of payments to private investigators contains “conspicuous and often shocking evidence”, according to lawyers for a group of claimants accusing the publisher of using unlawful techniques.

Prince Harry, Elton John and Doreen Lawrence are among the seven claimants in the 10-week, multimillion pound case against Associated Newspapers Ltd (ANL). The publisher denies all the claims.

In closing submissions, David Sherborne, the leading barrister for the claimants, said the court should conclude “the true scale” of unlawful information gathering at ANL “was enormous”.

“There would have been thousands of invoices underpinning these payments [to private investigators], all of which have been destroyed or not located,” he said.

“The difference between the known universe of payments to [private investigators], which is vast, and the small number of invoices which have been disclosed is stark in the extreme.”

In court, Sherborne said that one box containing records of payments to private investigators – which he called “Pandora’s box” – was only found by chance by a legal worker last year.

ANL said in its closing submissions that it had offered “demonstrably conscientious and generous approach to disclosure”. It said the company had handed over more than 2,700 documents.

Sherborne pointed to two examples in which the existence of documents had allowed the claimants’ legal team to draw a link to alleged unlawful activity. One related to a draft story about the actor Sadie Frost’s ectopic pregnancy, which was never published.

In this case, Sherborne said invoices relating to a private investigator showed that Katie Nicholl, the former Mail on Sunday journalist, had “an ongoing interest” in Frost.

He also pointed to records about another private investigator found in the “Pandora’s box”. He alleged they corresponded to detailed medical information about Frost recorded in Nicholl’s notebook. The claimants’ legal team say the information came from a “blag” carried out by the private investigator.

Nicholl has said the information came from a freelance journalist who had “a very, very good source” within Frost’s inner circle.

Sherborne said: “This is obviously one of a number of examples where we have direct evidence that can be linked, but that isn’t always the case. If we had that across all the articles, the exercise would be a lot simpler.”

He also pointed to a story about a holiday Prince Harry was taking with former girlfriend, Chelsy Davy, by the Daily Mail’s royal editor, Rebecca English.

The court had already been shown an email from private investigator Mike Behr containing Davy’s flight details. English has said the information was “never asked for and it was never acted upon”.

Sherborne said the email had not been revealed by ANL, but disclosed through separate litigation. He urged the judge to infer there was a culture of unlawful information gathering that had been concealed.

The claimants’ legal team are now focusing on four journalists – Nicholl, English, the former reporter Stephen Wright and the former Daily Mail showbusiness editor, Nicole Lampert.

ANL said the claimants had initially made “headline-grabbing allegations” of hacking, phone tapping and bugging in the hope that “disclosure would turn up material to support their widely pleaded allegations, and that Associated would settle”.

However, ANL’s legal team said the publisher had “pleaded a positive case denying each specific instance” of unlawful activity.

“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,” it said in a written submission.

Both sides continue to argue over the role of private investigator Gavin Burrows, who made alleged confessions of unlawful activity for ANL in a 2021 witness statement, only to later say the document had been forged by Graham Johnson, a former phone hacker who subsequently researched unlawful activity in the press.

The case continues.