Surrey police knew of allegations in 2002 that Milly Dowler’s voicemail had been hacked by the News of the World but failed to act, it was revealed today.

It was nine years later that the hacking scandal emerged. Senior officers were “afflicted by a form of collective amnesia” over the force’s failure to investigate the claim during the inquiry into the 13-year-old’s murder, a report found.

The hacking allegations led to a public outcry, the closure of the News of the World and the Leveson Inquiry into press standards.

Today the Independent Police Complaints Commission revealed that knowledge of the allegation that Milly’s phone had been hacked was well known to all ranks of the force in the first days of the hunt for Milly who went missing on her way home from school in Walton-on-Thames, Surrey, in March 2002.

However, no investigation was launched at the time and the IPCC said it could find no evidence or witnesses to explain why.

IPCC deputy chair Deborah Glass said: “We will never know what would have happened had Surrey police carried out an investigation into the hacking of Milly Dowler’s phone in 2002.

“Phone hacking was a crime and this should have been acted upon, if not in 2002, then later, once the News of the World’s widespread use of phone hacking became a matter of public knowledge and concern.

"Our investigation has heard from officers and former officers from Surrey police who have expressed surprise and dismay that it wasn’t investigated.

“We have not been able to uncover any evidence, in documentation or witness statements, of why and by whom that decision was made — former senior officers, in particular, appear to have been afflicted by a form of collective amnesia in relation to the events of 2002.