Officers believe they have discovered evidence of a widespread but previously unknown conspiracy centred on the News of the World features desk, indicating that phone-hacking was deeply ingrained throughout Rupert Murdoch's tabloid empire.
The development threatens to reignite the debate surrounding press misconduct on the day that MPs vote on rival plans to implement the regulatory proposals of Lord Justice Leveson.
Up to this point the Metropolitan Police's criminal investigation into alleged phone-hacking, Operation Weeting, has focussed on the now-defunct tabloid's news desk.
The fresh line of inquiry investigation stems from information provided by a former News of the World insider, whose identity is known to The Independent.
According to senior police, legal and political sources, the supergrass's evidence is thought to have led to the arrests in February of six former journalists who worked on the features desk of the NOTW, as well as the arrests last week of four current and former news executives from Trinity Mirror titles. Substantial sequences of email exchanges and phone contacts between the supergrass and former Fleet Street colleagues, provided Operation Weeting detectives with new information which forced a major rethink on the full scale of phone hacking and the numbers of victims who were targeted.
At a special hearing at the High Court today examining the current civil actions against News International over hacking, it will be revealed that more than 800 potential new victims have been identified as a result of the Met's shift in focus.
Last year the Met's then deputy assistant commissioner, Sue Akers, said that Operation Weeting had so far notified 2,500 people whose phones may have been illegally accessed.
That number could rise substantially due to the scale of the additional conspiracy. Lawyers associated with hacking actions are expecting a fresh flow of new claims against News International.
Information linked to the arrests last week of the Mirror Group journalists, is also likely to increase the overall number of potential new victims of phone hacking. Sources have told The Independent that the Met already have a preliminary list of victims they believe are victims of a hacking conspiracy that operated inside the Sunday Mirror.
The re-evaluation of the sheer scale of hacking as a Fleet Street practice is almost certain to be part of the debate inside the Commons today when MPs debate the merits and demerits of having press regulation enshrined in law. News International's admitted guilt on phone hacking and the record-breaking damages it has so far paid out to hacking victims, have centred mainly on the NOTW's news desk operations.
The alleged scale of a further conspiracy, that could yet prove to match the £300m hacking has so far cost the Murdoch-owned company, is already affecting the schedule for the criminal trials that were due to begin this September.
Lawyers in the High Court representing victims and the Metropolitan Police are understood to have already requested that the criminal trials be postponed until November.
Some lawyers believe the spring of 2014 is more realistic.
The supergrass's decision to turn Queen's Evidence and co-operate with the Weeting probe began in 2011, The Independent understands.
Computer equipment and a mobile phone belonging to the writer which the Met examined is alleged to have contained information which raised suspicions that phone hacking was not confined to news desk and the private detective which NOTW news executives regularly employed to oversee hacking.
The former News of the World staff arrested in February by police are understood to include the paper's former showbusiness columnist Rav Singh, ex-features editor Jules Stenson, former features journalist Matt Nixson and Polly Graham, a former showbusiness journalist.
The former Sunday Mirror staff held last week were that newspaper's ex-editor Tina Weaver; the current editor of The People, James Scott; Nick Buckley, The People deputy editor; and Mark Thomas, a former Sunday People editor. The People was formerly known as the Sunday People.
Last night Scotland Yard said they would not make any comment on the whether or not they were using a supergrass.
News International was contacted by The Independent last night, but declined to comment.
Hacking victims: payouts so far
Milly Dowler's parents £2m, plus £1m donated to charity
Revelations in 2011 that the News of the World had accessed the voicemails of the murdered teenager ignited the phone hacking scandal.
Gordon Taylor £700,000
The settlement in 2008 bound Taylor, the chief executive of the Professional Footballer's Association, to secrecy in an attempt to stop evidence of phone hacking reaching court.
Colin Stagg £15,500
The man wrongly accused of the 1993 murder of Rachel Nickell was among 17 claimaints, including the Duchess of York and Hugh Grant, whose claims were settled last month.
Jude Law £130,000
The actor was one of 37 people, including Lord Prescott and Sara Payne, to have their cases settled by the New of the World in January 2012, bringing the payout total to £10m.
Charlotte Church £300,000
The Welsh singer and her parents received the settlement, plus another £300,000 in costs, in February last year after the News of the World had "unlawfully obtained" and published medical information.
