Detectives are checking whether the mobile phone of the union leader Bob Crow was hacked by a private investigator working for the News of the World.
Sue Akers, Deputy Assistant Commissioner of the Metropolitan Police, told lawyers for Bob Crow, general secretary of the National Union of Rail, Maritime and Transport Workers (RMT), that his case was under active consideration in a new police inquiry.
Mr Crow reported his suspicions – that journalists may have had access to private information about his movements and his union's activities from 2000 – to police last month.
Ms Akers told his lawyers: "We have started a review of all material gathered to date, to ensure that we can complete a comprehensive and accurate analysis. This is clearly a major task and will take some time to complete. However, we are committed to sharing with your client any information that is relevant to him as soon as we are confident of the accuracy."
Ms Akers has criticised the previous police investigation into hacking carried out by Glenn Mulcaire for the News of the World. Lawyers are acting for 155 public figures who claim or who have been told that they were hacked.
Mr Crow said: "RMT welcomes the prompt response from the Metropolitan Police to the concerns over phone hacking that our lawyers have raised."