'News of the World' hacked Milly Dowler's phone when Rebekah Brooks was editor

The News of the World interfered with the police inquiry into the disappearance of the Surrey schoolgirl Milly Dowler by hacking into her mobile phone, police sources have confirmed.

In the latest blow to Rupert Murdoch's News International, Scotland Yard detectives have found evidence that the Sunday paper targeted the 13-year-old's mobile phone in March 2002, soon after she disappeared on her way home in Walton-on-Thames.

The tabloid – then being edited by New International's current chief executive Rebekah Brooks – deleted messages left on her phone by desperate friends and relatives to free space in her inbox, so that it could access fresh voicemails for stories. This led Surrey Police and the Dowler family to believe that she may still be alive.

The NOTW later ran a story based on a hoax message left on her voicemail and also carried a heartrending interview with the Dowler family, unaware that their false hope had been at least partly stirred by its own criminality. It is understood that the mobile phones of Milly's parents, Robert and Sally, were also targeted.

By then Milly had been murdered by Levi Bellfield, who was jailed for life last month after a trial that involved intense personal questioning of her parents.

Mark Lewis, their solicitor, said last night that the Dowlers had been informed about the phone hacking by officers from Operation Weeting, the Yard's new investigation into phone hacking by the private investigator Glenn Mulcaire. Mr Lewis said: "I would suggest this is one of the worst cases of all. You have to ask the question: who at the News of the World was thinking it was appropriate to try to hack into the phone of a missing young girl?" He added: "Sally and Bob Dowler have been through so much grief and trauma without further distressing revelations to them regarding the loss of their daughter."

The latest twist in the long-running scandal is likely to increase the pressure on Ms Brooks, who used her editorship of the NOTW to conduct a campaign to tighten laws to protect children from paedophiles following the murder of Sarah Payne in 2000.

The Labour MP Tom Watson claimed last week that the NOTW hacked the phones of the parents of Holly Wells and Jessica Chapman, the children murdered at Soham in 2002. Last night, he told the Commons that targeting Milly Dowler's phone was a "despicable and evil act that will shock parents up and down the land to the very core".

Chris Bryant, another Labour MP and prominent campaigner, said: "This is the most horrific, depraved story yet in this catalogue of extensive criminality. Not only did the News of the World clearly think that they were above the law, they were prepared to play God with the emotions of the Dowler family."

Yesterday, it was confirmed that detectives from Operation Weeting had also visited Colin Stagg, the man wrongly accused of murdering Rachel Nickell on Wimbledon Common in 1992, to inform him there was evidence that Mulcaire may have hacked his phone as far back as 2000.

The Independent established earlier this year that the Dowlers had been targeted by another private investigator, Steve Whittamore, on behalf of News International. With the help of an accomplice, he supplied the NOTW with the ex-directory number for the Dowlers' home.

Detectives are believed to have found evidence of the Dowlers' private information in the 11,000 pages of notes kept by Mulcaire. Upon finding the missing schoolgirl's voicemail inbox to be full, The Guardian reported last night, the NOTW decided to delete messages in order to allow more to be left – which could then provide leads for stories.

News International said: "This particular case is clearly a development of great concern and we will be conducting our own inquiries as a result."