A woman has admitted making up a horrific story about how she was brutally raped on an Oxfordshire road - a lie which wasted 600 hours of police time.

Lisa Fraser, 27, of Barrington Road, Watchfield, near Shrivenham, has been formally cautioned for the false claim which sparked a major police investigation and spread fear among local residents.

Fraser claimed she was enticed from the Swindon-bound carriageway of A420, near Buckland, by a distressed person between 9.15pm and 9.45pm on Monday, November 28 last year.

She told police a man wearing a balaclava jumped out from bushes and threatened her with a knife before she was dragged into the bushes and raped.

Police then launched a massive operation, searching neighbouring fields, the lay-by and interviewing hundreds of motorists. Part of the A420 westbound was closed while forensic checks were carried out.

Fraser was initially charged with making a false rape claim and was to stand trial before District Judge Brian Loosley at Wantage Magistrates Court on September 15.

Det Sgt Chris Biddle of Abingdon CID said: "I would like to reassure the community of Buckland that we are now sure that no such incident took place."

He said various factors had led to the decision not to go ahead with Fraser's trial, but would not reveal them.

He said: "This was a serious allegation and wasted a considerable amount of police time and resources as well as frightening people in the local community.

"While we actively encourage any victim of a genuine crime to come forward, anyone who makes a false accusation such as this could be arrested and face court proceedings."

Police spokesman Victoria Bartlett said: "The woman has received a formal caution, and the decision to take this action was made in liaison with the Crown Prosecution Service."

* Last November, two Bicester 16-year-olds, who cannot be named for legal reasons, were jailed for falsely claiming they were abducted and raped.

They pleaded guilty to perverting the course of justice and wasting police time after sparking an investigation which involved four police forces and cost £100,000.

They made up a story about being raped at Glory Farm Park, Bicester, in September last year in an incident unrelated to yesterday's development over the A420 rape claim.

Then in February they phoned police, friends and relatives, saying they had been abducted and were being held prisoner in Oxford, where they had been assaulted, raped, forced to take drugs and bitten.

One girl got eight months for perverting the course of justice and four months for wasting police time. The second got six months and four months respectively.