A private detective working for the News of the World is accused of hacking into Milly Dowler's voicemail after she went missing, a lawyer for the murdered schoolgirl's parents said today.
Scotland Yard officers contacted Sally and Bob Dowler about the allegations in April, a month before Levi Bellfield went on trial for her murder, solicitor Mark Lewis said.
Private investigator Glenn Mulcaire is alleged to have illegally accessed Milly's phone messages after she was abducted by Bellfield as she walked home from school in Walton-on-Thames, Surrey, in March 2002.
Mr Lewis, from London-based Taylor Hampton Solicitors, said: "Sally and Bob Dowler have been through so much grief and trauma without further distressing revelations to them regarding the loss of their daughter.
"It is distress heaped upon tragedy to learn that the News of the World had no humanity at such a terrible time.
"The fact that they were prepared to act in such a heinous way that could have jeopardised the police investigation and give them false hope is despicable."
Mr and Mrs Dowler are now pursuing a claim for damages against the News of the World, Mr Lewis said.
Scotland Yard and the News of the World's publishers, News International, declined to comment on the allegations.
Mulcaire and former News of the World royal editor Clive Goodman were given jail terms in January 2007 after the Old Bailey heard they plotted to hack into royal aides' telephone messages.
Bellfield, 43, was given a second whole life jail term last month for 13-year-old Milly's murder.
But her parents said they felt as though they themselves were "put on trial" by his defence, which saw them face intrusive questioning about their family life in the witness box.
News of the World journalists are accused of deleting some voicemail messages on Milly's phone in the first days after she vanished, leading her relatives and friends to think she could still be alive, the Guardian reported.
Speaking in Parliament, Labour MP Tom Watson condemned the alleged hacking of the murdered teenager's phone as a "despicable and evil act".
It also emerged today that police have contacted Colin Stagg, the man cleared of murdering Rachel Nickell, and entrepreneur Sir Richard Branson to tell them they may have been victims of News of the World phone hacking.
Detectives have told Mr Stagg his phone was hacked in 2000, six years after a judge at the Old Bailey threw out the case against him, his solicitor Alex Tribick said.
Mr Tribick added: "From my understanding, this is linked with the year 2000, which I believe is the earliest date of anybody so far."
Mr Stagg and his lawyer have yet to meet officers from Operation Weeting, Scotland Yard's fresh investigation into phone hacking allegations, but they are planning to make a civil claim for compensation.
Sir Richard wrote on Twitter: "Police inform me News of the World journalists targeted my phones. I should have been more entertaining!"
He suggested he would also pursue a claim for damages to be donated to charity, adding: "Hopefully good causes will be the winner."
Operation Weeting detectives have arrested five people since the new inquiry was set up in January.
A number of celebrities are pursuing litigation against the News of the World in the High Court.
They include ex-footballer Paul Gascoigne, actor Jude Law, sports agent Sky Andrew, interior designer Kelly Hoppen and MP Chris Bryant.
Others, among them actress Sienna Miller and football pundit Andy Gray, have already settled with publishers News Group Newspapers.
A News International spokesman said: "We have been co-operating fully with Operation Weeting since our voluntary disclosure in January restarted the investigation into illegal voicemail interception.
"This particular case is clearly a development of great concern and we will be conducting our own inquiries as a result. We will obviously co-operate fully with any police request on this should we be asked."