Detectives carrying out the investigation into illegal newsgathering techniques at Rupert Murdoch's British newspaper group have been asked to investigate whether it attempted to blackmail politicians.
The alleged plot centres on News International's apparent efforts to warn off MPs on a parliamentary committee from disproving its discredited defence that phone hacking was the work of a single "rogue reporter".
According to the former senior News of the World journalist Neville Thurlbeck, News International ordered the Sunday paper's reporters to scour the private lives of MPs on the Commons Culture, Media and Sport Committee in 2009. At the time, Mr Murdoch's company was mounting what it now admits was a mistakenly "aggressive" response to allegations that the interception of voicemail messages was rife.
On the advice of the parliamentary authorities, the Labour MP Tom Watson, pictured, has now asked the Metropolitan Police to investigate. According to Mr Thurlbeck, reporters were told by those in "deepcarpetland" to obtain evidence of affairs or gay relationships.
In the New Statesman this month, he added that the NOTW's journalists had been so concerned about the exercise that they did not carry it out, but went further than he had previously about its intent, Mr Thurlbeck wrote: "The objective was to find as much embarrassing sleaze on as many members as possible in order to blackmail them into backing off from its highly forensic inquiry into phone hacking."
In a letter to the Deputy Assistant Commissioner leading the Met's inquiries into News International Mr Watson wrote: "If these allegations are found to be true, it suggests there was a conspiracy to blackmail."
Yesterday the Met said it was unable to comment on the MP's request.
Mr Thurlbeck, arrested on suspicion of phone hacking, remains on police bail. News International made no comment on Mr Watson's letter.