The Metropolitan Police blocked legal action aimed at identifying all the alleged victims uncovered by its criminal investigation into phone hacking by the News of the World.
Documents filed at the High Court in London show that Scotland Yard is resisting a claim for a judicial review of its handling of the case, on the basis that it does not have a public duty to contact everyone brought to the attention of detectives.
The legal action, brought by two senior politicians, a former policeman and a journalist, is aimed at forcing the Met to disclose the names of all the "interested parties" connected to the original investigation, which led to the convictions of the newspaper's royal correspondent, Clive Goodman, and a private investigator, Glenn Mulcaire.
Estimates of the potential number of victims range from a "handful" to several thousand, each of whom may have a claim for damages against the News of the World, then edited by Andy Coulson, now David Cameron's director of communications.
Lawyers estimate that even if the final number turns out to be more conservative, the legal bill facing the Sunday newspaper's owners will still run to tens of millions of pounds. Labour MP Tom Watson claimed last night that the News of the World's parent company, News International, had already paid out millions of pounds to settle the victims' claims, and millions more on legal teams to defend the cases.
He said: "I don't think it's unreasonable for News International to say why they are paying legal fees for Andy Coulson and Glenn Mulcaire from half a decade ago."
In a separate move, Scotland Yard complied with a court order to hand over inquiry documents to lawyers acting for the sports agent, Sky Andrew. The documents, some of which may be redacted, are understood to have been found by police among the papers and correspondence of Mulcaire in 2006, when his home and office were raided in their investigation into phone-hacking.
The judicial review case, which is being spearheaded by former deputy prime minister John Prescott, Chris Bryant MP, former senior Met policeman Brian Paddick and journalist Brendan Montague, is expected to be granted permission to proceed in the next few weeks.
Tamsin Allen, a partner at London law firm Bindmans, who is representing the four, said if the case is given the go-ahead the courts will need to decide how wide an area the review should cover. "We want the Met to tell us the number and names of all the known and unknown interested parties to the investigation," she said. "But we also want the court to look at the decision-making process of the Met, and particularly why the scope of the inquiry was not widened to include all the interested parties."
In a summary of its defence, the Met argues that it has unfettered discretion in deciding how it conducts investigations and the appropriate use of its limited resources. It says it has no obligation to contact all the "interested parties".
The four argue that the failures in the investigation are an ongoing breach of Article 8 of the European Convention on Human Rights and that the Met had a positive duty to warn those victims so that they could take appropriate action to protect themselves.
Last week, News International said a senior News of the World executive, Ian Edmondson, had been suspended over allegations of professional misconduct believed to be linked to hacking. The newspaper is believed to have paid out large sums to Gordon Taylor, the chairman of the Professional Footballers' Association, and to the publicist Max Clifford. The actress Sienna Miller is suing the paper's parent company and the private investigator.
A Scotland Yard spokesman said that its enquiries into to the phone hacking were "ongoing" but that officers "were not prepared to discuss" any of the civil cases before the courts.