A specialist unit set up by Scotland Yard to investigate sexual assaults has been severely criticised for failing to properly manage a rape allegation by a 15-year-old girl.

In a damning report the Independent Police Complaints Commission has found that there were “significant errors” made during the inquiry by the much-vaunted Sapphire unit in Southwark.

Although someone was charged in connection with the serious sexual assault, he was acquitted after a trial. The report says that during the court case “it became clear that a number of errors had been made by the police”.

The criticism comes just days after John Worboys, a London taxi driver, was found guilty of a series of sex attacks on 12 women. The Times revealed that 12 women went to the Metropolitan police to complain about a taxi driver but their allegations were never linked by Sapphire teams.

They also missed an opportunity to stop Worboys in July 2007 when he was arrested and then set free.

Control of the Sapphire units, launched in 2001 to set the standard in rape investigations, has now been taken from borough level and placed under the control of the Homicide and Serious Crime Command at Scotland Yard.

In the current inquiry a police constable was allocated to the case even though the investigation should have been headed, at the very least, by a detective constable.

Three officers will be given written warnings and a fourth will receive words of advice for their part in the rape investigation failures.

The IPCC found that forensic opportunities at the scene were never explored, there was a failure to identify and arrest the suspect at the earliest opportunity and there was also a failure to properly and effectively supervise the investigation after the teenager reported the matter to police in February 2005.

The police also failed to properly examine the girl’s mobile telephone, only looking at the numbers stored in her phone rather than requesting the full billing list to see who had called her.

By the time they did the records were no longer available.

Amerdeep Somal, the IPCC commissioner, said: “The report into this investigation highlights that significant errors were made that compromised the quality of the investigation into a very serious offence.

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