Scotland Yard has accepted for the first time the extent of the phone-hacking scandal when it told a court the number of potential victims whose voicemails were targeted by the News of the World is likely to be "substantially" more than 91.

A high court hearing to timetable and organise the growing civil claims for damages against Rupert Murdoch's News International heard that the new police investigation believed the scale of potential victims was much higher than leading officers had previously said.

Previously the Metropolitan police said they had found a total of 91 pin numbers – necessary to access a mobile phone's voicemail – in the possession of the private investigator Glenn Mulcaire.

But Jason Beer QC, representing the Met, told the hearing the number of potential victims is "substantially" higher than 91. "It is wrong to say that 91 is the answer, that that is the maximum [number of victims]. It may be on a bigger scale."

In other developments:

• The judge, Mr Justice Vos, recommended that four test cases for those alleged to have been victims of hacking – Sky Andrew, Kelly Hoppen, Sienna Miller and Andy Gray – should be heard no later than February 2012.

• News International said it had offered Miller £100,000 in damages for the repeated hacking of her phone.

• Her former partner, Jude Law, was set to issue his own proceedings, the high court heard. The actor's spokeswoman refused to comment.

• Comments made eight years ago by Rebekah Brooks, now News International's chief executive, could prompt a further criminal inquiry led by the Met.

Detectives are still trawling through 9,200 pages of mainly handwritten material seized from Mulcaire, who was convicted of intercepting voicemail messages in January 2007, along with the News of the World journalist Clive Goodman.

During the original investigation, police seized paperwork and records from Mulcaire, who was employed by the tabloid.

John Yates, the Met's acting deputy assistant commissioner, who handled a previous phone-hacking investigation, said that the police had only identified 10 to 12 victims. The fresh investigation team is under the leadership of deputy assistant commissioner Sue Akers.

Yates said earlier this month that he had quoted the figure on at least four occasions because prosecutors had told police they needed to prove not only that voicemail had been intercepted but also that this had been done before the messages had been heard by the intended recipient. That claim was contested by Keir Starmer QC, the director of public prosecutions.

In a letter to the Commons home affairs select committee, Yates said lack of first-hand knowledge may explain why he and Starmer gave different accounts of the legal advice.

"Both Keir Starmer and I are conscious that we are somewhat hindered in our efforts to assist your committee further in this matter by the very fact of our not being involved in any way until we came into our current posts – in my case in 2009."

Beer, the Met's lawyer, said that since last week, when News International admitted liability in eight cases, police had been "flooded" with people inquiring if they might have been victims of what lawyers of the victims described yesterday as a "conspiracy".

Michael Silverleaf QC, for News Group Newspapers, said the £100,000 the company had offered Miller was the maximum she could expect to win.

"She cannot realistically recover more than we are offering," he told the judge. "The civil litigation process does not exist for people to vent their feelings in public. It provides a remedy for wrongs. We have admitted the wrong and agreed to pay her the maximum sum."

The offer was made on 6 April. Miller's team indicate her action is "continuing" and that she wants to find out exactly what the NoW did, which so far, her legal team says, the newspaper is refusing to do.

Although the company's offer of damages is higher than the £20,000 to £70,000 that many had expected the cases to settle at, the extra sum reflects the fact that Miller had been making claims of breach of privacy and harassment, and that any damages owing to phone hacking were only part of that sum. The actor had also been heavily targeted by the News of the World.

At the hearing, lawyers for the victims claimed that calls to hack the voicemails had been made from phone numbers registered to the paper.

A News International spokesperson said: "We made clear last week that our intention was to apologise and to deal with these cases in the most fair and efficient way possible. We believe the judge's recommendations support that."

A lawyer for one of the hacking litigants, who asked not to be named, said the hearing had gone badly for the publisher.

The lawyer said: "News Group have suffered a devastating blow today to their latest strategy to close down the phone-hacking litigation.

"The judge entirely rejected their contention that their narrow 'admissions' were sufficient to bring all the liability issues in the nine leading cases to an end and ordered a trial of the generic issues, including whether they entered into a conspiracy with Glenn Mulcaire to hack voicemails."

Last week, police arrested the NoW's chief reporter, Neville Thurlbeck, and its former head of news, Ian Edmondson.

On Thursday a senior reporter, James Weatherup, became the third journalist who had worked at the newspaper to be questioned and released on police bail.