New criticism of Scotland Yard's handling of the affair was triggered by the disclosure of court documents appearing to link another senior newspaper executive to the illegal operation. News of the World suspended its assistant editor, Ian Edmondson, on Wednesday after an allegation of professional misconduct.
It emerged last night that Scotland Yard had known of evidence against Mr Edmondson four years ago when officers were investigating the paper's former royal correspondent Clive Goodman and private investigator Glenn Mulcaire, who were both convicted of unlawfully intercepting telephone calls in 2007. Asked yesterday why it had not questioned Mr Edmondson, the Met refused to comment, but a source said that senior figures at the Yard had resisted broadening the investigation.
Last night the Crown Prosecution Service declined to say whether its lawyers had been sent the "new" evidence yet by the police.
Chris Bryant, the shadow minister for Constitutional Reform, said the investigation risked "bringing the Met into disrepute" and that it would be better carried out by another force.
"My concern all along has been that the Met hasn't done a full investigation. It hasn't notified many hundreds of people who were the subject of investigations by Mr Mulcaire, even though the police had that information for years."
Mr Bryant, who is bringing his own hacking claim against News of the World, added: "It hasn't interviewed Ian Edmondson; it hasn't interviewed anybody else at [the paper]. You start to wonder if there's a reason for that."
The revelations brought the case a step closer to Andy Coulson, who was editor of the red-top paper at the time and is now David Cameron's most senior media adviser.
Labour's Home Affairs spokesman, Ed Balls, called for an independent force to look into the Met's investigation of phone hacking, and whether it had been sanctioned by more senior staff, including Mr Coulson.
Brian Paddick, a former senior Metropolitan Police officer who is taking legal action over allegations that his phone was hacked, told The Independent last night: "When the police are forced to disclose information by court order then it tends to raise doubts about whether the case has been properly investigated or not."
Mr Balls said: "As more information comes out it's getting closer and closer to Mr Coulson. The more we see of this matter, the more it looks very murky, and it does raise the real question: what is David Cameron doing keeping Andy Coulson in No 10?"
The latest documents lodged at the High Court in London appear to link Mr Edmondson with the interception of voicemail messages from the phone of the actress Sienna Miller.
Her lawyers said the paperwork and other records seized by police from Glenn Mulcaire's home address show that the police must have known it was likely that phone hacking was not the work of one "rogue reporter" as the paper claimed at the time.
Ms Miller is suing News of the World's parent company, News Group, and the private investigator, accusing them of breaching her privacy and of harassment. The newspaper said that "appropriate action" would be taken if the allegation were proven.
The paper has said the 2007 case was a one-off, but police revived an investigation into the hacking scandal in September after one of its former journalists claimed Mr Coulson had encouraged him to hack voicemails. Mr Coulson agreed to be interviewed by the Met in November over the claims.
The Director of Public Prosecutions, Keir Starmer QC, said last month there was no evidence to bring charges over phone-hacking claims at the paper, after several witnesses refused to testify. These included Sean Hoare, the journalist cited in The New York Times as making the allegation.
A spokeswoman for the Crown Prosecution Service said its lawyers were aware of the media reports concerning Mr Edmondson but that it was "inappropriate to comment on them any further". The former Scottish Socialist leader Tommy Sheridan is suing News International and Scotland Yard after his personal details emerged as part of the phone-hacking scandal.
PM irritated by coulson inquiry
David Cameron tried to deflect questions about Andy Coulson yesterday by launching a personal attack on Labour's Shadow Chancellor, Alan Johnson.
Mr Johnson, who was Home Secretary when police began to investigate the scandal, said that the affair has a "long fuse" that will eventually blow up under the Prime Minister's press chief. "The concern was whether Her Majesty's Inspector of Constabulary had the resources to carry out an independent inquiry," said Mr Johnson yesterday.
"My instinct was that we needed an independent inquiry, but the general election intervened. I'm not rushing into allegations about this but there is a very long fuse on this, and I believe that [it] leads to Andy Coulson."
The Prime Minister appeared irritated to be quizzed on the subject yesterday and referred to a photograph in Wednesday's Daily Mail of Mr Johnson being treated to an expensive meal by a lobbyist, with a glass of champagne and a glass of wine on the table.
"Probably he said this over a long lunch," Mr Cameron said. "I don't know if he was asking this question after one bottle of claret or two – or was it pink champagne? When he answers that, I'll come back to him."
