OXFORD’s police are failing to hit targets for the number of rapists they prosecute and have the worst record in the Thames Valley.

Just one in eight reported rapes in the city resulted in a caution or a charge against a suspect between April and September last year.

But police said the low results were because the overall number of victims feeling confident enough to report rapes had gone up following Operation Bullfinch, launched to tackle sexual exploitation in Oxford.

And one leading officer stressed some investigations could be long and complex.

Detective Chief Inspector Mark Johns said: “For other offences it’s not in the best interests to take it to court.

If there are victims that don’t want to go through the trauma of a trial we balance their wishes with our desire to prosecute. Then there are others where we have evidential difficulties when referring it to the Crown Prosecution Service and some of those don’t get to court.”

He added: “Lots of these rapes are historic, they happened years or months ago.”

Thames Valley Police was unable to say what proportion of the reported rapes were historic.

When asked for a comment CPS spokeswoman Louise Rosher said they were unable to comment on the police figures because they did not include how many cases had been referred to the CPS. 

Former Chief Constable Sara Thornton and Police and Crime Commissioner Anthony Stansfeld set the force’s “outcome” goals: the number of cases where suspects are charged or cautioned.

For rape, the goal was an outcome rate of 23 per cent.

But Oxford achieved just 12.8 per cent, the lowest in the area. The average across Thames Valley was 22.9 per cent, a drop of one per cent from the same time in 2013.

The highest was Aylesbury, with 44 per cent.

Home Office figures released in January showed there were 47 rapes reported in Oxford between April and September 2014, up from 23 in the same time period in 2013.

Across Oxfordshire, reported rapes rose from 79 to 147.

DCI Johns said of the rise: “That’s why we’ve struggled to work towards that target.

The increase is down to a number of factors including the increase in historic reporting. Rapes are investigated the same way across Thames Valley.”

He said he was “pleased”

the number of reported rapes increased, and said: “It sends a message that people are confident in reporting rapes.”

He added high-profile cases such as Operation Bullfinch, where more than 370 children were identified as being at risk of sexual exploitation in Oxfordshire , have boosted the confidence of victims.

Oxford Sexual Abuse and Rape Crisis Centre director Lisa Ward said: “If people have a sense of trust in the system then that can only be a good thing. It is really, really difficult to figure out why people might be coming forward.”

She warned victims could be put off reporting crimes if outcome rates did not improve.

Mr Stansfeld was unavailable for comment.