Last week, the paper accepted responsibility for intercepting Sienna Miller's voicemail messages, between 2004 and 2006, but it has assiduously challenged assertions that offences were committed outside that period.
But this paper can reveal that at least three complainants refer to hacking either before or after those dates, and one goes back to 2001, when Rebekah Brooks, now chief executive of News International, was editor of the News of the World.
Last night, Andy Gilchrist, the former Fire Brigade Union leader, said: "I have seen papers in the police's possession from the original Mulcaire haul [the private detective jailed for hacking royal aides' phones] that strongly suggest my phone was hacked into. Further, these papers clearly are marked with dates relating to 2001, 2002 and 2003. I have written to formally request copies of this documentation from the police."
Mr Gilchrist was the subject of extensive coverage in The Sun, the News of the World's sister paper, when his union was on strike. The Sun ran a story headlined "Fire strike leader is a love cheat" during the first week of its editorship by Ms Brooks. News International has always vigorously denied, and continues to deny, that the unlawful activity extended beyond the News of the World.
Other cases against the newspaper are also believed to lie outside the "inclusion zone", including that of Ulrika Jonsson, formerly a columnist on the paper, and Jude Law. The police also have evidence that the phones of the parents of the Soham schoolgirl Jessica Chapman, murdered in August 2002, were hacked.
A News International spokesman said: "We are aware there are potential claims against us from 2003. It was the principle of the apology that we made in April that was important, not the timescale."
The news comes at the end of a week when two new dimensions to the scandal emerged, enveloping both other newspapers and different nefarious methods. It was claimed that Jonathan Rees, a private investigator, had been employed by newspapers other than the News of the World – including the Daily Mirror – and had committed unlawful acts.
Peter Mandelson has asked police to look into whether his bank account was hacked into. Lord Mandelson's concerns relate particularly to 1998, the time of press interest in his mortgage. Piers Morgan, previously editor of the News of the World, edited the Mirror from 1995 and 2004, and friends of the peer note that the pair have never been close.
In a further twist, Alastair Campbell, Tony Blair's former press aide, last night sent Mr Morgan, who boasted of having broken the story of Cherie Booth's pregnancy, a message via Twitter: "Congrats re pregnancy. Btw what exactly did Jonathan Rees give you for the thousands he got from Mirror re me, Peter M, etc?"
Yesterday, it was reported that the England captain, John Terry, had a tracking device planted in his car, and the former Tory party treasurer Lord Ashcroft claimed that more than a decade ago a private investigator had "blagged" his way into the Conservative Party's bank account.
"Some time later," he wrote on the ConservativeHome website, "I discovered that a private detective... had successfully – and, again, illegally – obtained details of my private tax affairs from the Inland Revenue. These were details that eventually found their way into the pages of The Sunday Times."
How the inquiry grew: Accusations, denials and apologises along the way
February 2007 News of the World reporter Clive Goodman and private investigator Glenn Mulcaire are jailed for illegally intercepting voicemail messages. The editor Andy Coulson resigns.
July 2007 Gordon Taylor sues NoW. In documents submitted to court, News Group executives say the company had not been involved in Mulcaire's hacking activity. They deny possessing any record of illegally intercepted messages.
July 2009 Before a Commons select committee, Andy Coulson says he is "absolutely sure" that Goodman was a "rogue case".
September 2010 Coulson "emphatically denies" fresh allegations from a former reporter that he presided over a culture of phone hacking while he was editor.
December 2010 Before open court, at the trial of Tommy Sheridan, Coulson again denies there was a "phone hacking culture" at NoW.
January 2011 NoW news editor Ian Edmondson is sacked. Police launch a new investigation. Coulson quits his Downing Street job, but "stands by" previous denials on phone hacking.
April 2011 Facing dozens of civil actions from alleged phone hack victims, NI makes "unreserved apology" and admits liability for "some" of the cases against it, but insists it will contest other cases.
Charlie Cooper
