Documents linked to a former News International executive can be searched over claims Rupert Murdoch’s media company falsely implicated Gordon Brown and Tom Watson in a “fake security threat” to “justify” the deletion of millions of emails, the high court heard.

News Group Newspapers (NGN), publisher of the Sun and defunct News of the World, faces accusations it created a “false narrative” that the Labour peer Lord Watson conspired with the ex-prime minister to obtain stolen data as part of a bid to conceal wrongdoing and “subvert” police investigations into the phone-hacking scandal.

Will Lewis, now CEO of the Washington Post, was group general manager of News International at the time of Operation Weeting, the Metropolitan police investigation into phone hacking in 2011.

On Monday, judge Mr Justice Fancourt was told that in the Met’s minutes of a meeting between detectives and Lewis on 8 July 2011, it was recorded Lewis had told them: “We got a warning from a source that a current member of staff had got access to Rebekah’s [Brooks’] emails and had passed them to Tom Watson MP.

“This came to Rebekah. I was asked to meet the source. I will consult with BCL [lawyers] as to whether I can tell you the identity of the source. The source repeated the threat. Then the source came back and said it was a former member of staff and the emails had definitely been passed and that it was controlled by Gordon Brown. This added to our anxieties. We took steps to try and be more specific around her emails.”

NGN denied that the 2011 security threat over the suspected theft of chief executive Brooks’s emails was devised as part of a “cover-up”. In written arguments, Anthony Hudson KC, for NGN said the “threat” to Brooks’s data was “believed to be genuine”. He added: “NGN received information on two occasions that there was a direct threat that a current or former employee was actively trying to sell data belonging to NGN.

“It was against this background that NGN decided that multiple copies of confidential data should not be held in various systems, which would increase the risk of loss of data.”

The judge was told that the publisher, which had initially objected to making searches for potentially relevant material linked to Lewis and James Murdoch, the former executive chairman and others, had now agreed.

It came during a preliminary high court hearing over claims brought by Watson and the ex-Liberal Democrat business secretary Sir Vince Cable. Both former ministers allege NGN targeted them through voicemail interception and the use of private investigators.

In written arguments, David Sherborne, for Watson, said the politician was a target for NGN’s “unlawful activities” as a member of the culture, media and sport select committee which was investigating media malpractice.

“Lord Watson was also (falsely) cited by senior NGN executives, such as Rebekah Brooks and Will Lewis as part of the ‘fake security threat’ used to ‘justify’ the wiping of the crucial back-up tapes of NGN’s email system, that led to the deletion of millions of incriminating emails, as the claimants allege.”

Sherborne said of the “security threat” allegations: “It is difficult to think of a more serious aggravating factor than a claimant being deliberately scapegoated by a defendant as engaging in a conspiracy to illegally obtain data while using it as a fake excuse to unlawfully destroy potentially incriminating evidence relating to the same defendant’s acts of illegally obtaining information. This is particularly so where one of the scapegoats is a senior politician tasked by parliament with investigating media standards (and the other is a former prime minister).”

In Cable’s claim, the publisher is accused of unlawfully obtaining covert recordings of his constituency surgery in 2010 where he said he had “declared war on Murdoch”.

Cable alleges that the recordings, obtained by a Daily Telegraph “sting”, were leaked to the BBC by Lewis, documents said. The BBC’s report of the comments led to then prime minister, David Cameron, stripping Cable of responsibility for adjudicating on NGN parent company News Corp’s bid for full ownership of broadcaster BSkyB.

Lawyers for Watson and Cable asked the judge to order NGN to conduct further searches of material that may disclose evidence relevant to their cases.

NGN opposed some of the disclosure search bids as “disproportionate” and an “expensive and time-consuming” process, while agreeing to some searches. Hudson said there had already been “vast” disclosure in the legal action, adding that some wider searches for material were “disproportionate” when both claims were valued at less than £100,000, with both men incurring legal costs higher than this in their disclosure bids.

The hearing continues.