Insufficient evidence, lost files, and a lack of preparation were amongst the reasons for 71,000 ineffective pre-trial court hearings blamed on the Crown Prosecution Service (CPS), according to the report by spending watchdog the National Audit Office.

"The cost of this ineptitude goes beyond wasted cash," said Edward Leigh, chairman of parliament's Public Accounts Committee.

"The innocent suffer avoidable duress, they are even kept in custody longer than necessary. And, to put it bluntly, some guilty people must be getting away with their crimes scot-free.

The CPS, which has an annual budget of 568 million pounds, prosecutes 1.25 million people for criminal offences every year, the vast bulk (92 percent) in magistrates courts.

The NAO said 28 percent of all pre-trial hearings -- 784,000 cases a year -- were ineffective.

The defence were responsible for most of these and also for the majority of failed trials.

However, it said mistakes by the CPS and the police were responsible for 165,000 ineffective pre-trial hearings and that one in 10 of all failed trials could be attributed to the CPS alone.

Many problems stemmed from having individual prosecutors dealing with large number of cases, meaning they had little time to prepare so hearings could not go ahead as planned, the report concluded.

It also found there was insufficient oversight of cases by the CPS, meaning urgent cases were not always prioritised, as well as problems caused by the police and the courts themselves.

Citing one example, the report said: "The police had lost contact with the complainant, but the Crown Prosecution Service allowed the case to continue for another three months until the trial date, when the case was finally dismissed after 10 hearings.

The NAO said the CPS needed to reorganise its systems to free up more time for lawyers.

"The Crown Prosecution Service is making efforts to improve its performance in magistrates' courts but needs to do more to modernise the way in which it prepares and bring cases to court," said John Bourn, head of the NAO.