The Metropolitan police holds evidence that could prove hundreds of people had their phones hacked by the News of the World, Scotland Yard told the high court, a far greater number than had previously been believed.

Barristers for the Metropolitan police said notes seized from Glenn Mulcaire, the private investigator on the paper's books, showed he made a note of 149 mobile phone pin numbers and around 400 unique voicemail numbers. Both are used to access messages left on mobile phones.

Jason Beer QC, for the Metropolitan police, told a high court hearing the figures were: "a snap shot in time as of last week". Until Friday, the police had maintained Mulcaire kept a record of just 91 pin numbers.

The true extent of the investigator's activities is only now becoming apparent as Operation Wheeting, the new police investigation into phone-hacking at the News of the World which began in January, continues. Mulcaire's targets included the actor Jude Law, who is suing the paper for breach of privacy.

Law's case was joined the list of test cases that will be tried next year, along with that of Labour MP Chris Bryant, a former Europe minister.

Justice Vos, the judge assigned to take charge of all the hacking claims, said they would be added to three other test cases which were chosen last month – those of the agent Sky Andrew, interior designer Kelly Hoppen and football pundit Andy Gray.

Law's former girlfriend Sienna Miller was also scheduled to have her case against the News of the World heard next year but she indicated last week she would accept damages of £100,000 from the paper's publisher, News Group Newspapers.

The damages that will be awarded in each of the fives test cases, should they be successful, are likely to vary because each of them alleges a different level of criminal wrongdoing by Mulcaire and the News of the World.

Vos raised the prospect of imposing exemplary damages on parent company News International. They are set at a level high enough to punish the company for its behaviour and deter others from committing the same crime, and are often a percentage of a company's profits.

"It's one thing for a journalist to say 'I'm desperate to get a story'," Vos said. "It's another thing for the chief executive of a company to say 'I'm desperate to make more money by getting stories in this evil way'."

Vos added: "Was there a conspiracy between Mulcaire and News Group Newspapers to intercept voicemail messages? The answer is yes there was. Was it an agreement between the board of directors of NGN? ... I will have to determine the answer."