Scotland Yard said yesterday that a retired officer had told them that he had investigated Savile in the 1980s while based in west London but did not have the evidence to proceed.
Commander Peter Spindler said he believed the allegation was of an indecent assault, possibly in a caravan on BBC premises in west London, but officers have still not found the original file.
Another allegation, of inappropriate touching dating back to the 1970s, was made by a woman in 2003, but this was treated as “intelligence” by police because the victim did not want to take action.
Surrey Police submitted a file to the Crown Prosecution Service containing references to four potential offences, including an allegation of indecent assault on a young girl at a children’s home.
The allegations related to three potential victims in Surrey and another in Sussex, and Savile was interviewed under caution in 2009, but prosecutors decided there was insufficient evidence to bring charges.
The seventh allegation emerged in 2008 when Jersey police received a claim that an indecent assault occurred at children’s home Haut de la Garenne in the 1970s. Again it was decided that there was insufficient evidence to proceed.
Scotland Yard is leading the current investigation into accusations of abuse, which now involve around 300 potential victims.
Mr Spindler said Savile was “undoubtedly” one of the most prolific sex offenders he had come across.
He added: “Within London we have trebled the number of historic abuse allegations. I have no doubt that we’re in a watershed moment for child abuse investigation, and Operation Yewtree will be a landmark investigation.”
Claims have been made that former DJ Savile, who died last year aged 84, targeted children while they were in hospital.