Hundreds of victims of sexual and violent attacks in Bedfordshire were left with their cases unresolved after almost 50 per cent of prosecutions for sex crimes and offences against the person failed.

Bedfordshire came bottom of the first, unofficial league table of the Crown Prosecution Service’s 42 regional teams in England and Wales, with an overall conviction rate of 76 per cent.

The performance measurement, compiled from casework data spanning an 11-month period, placed Warwickshire on top with a 93 per cent success rate.

The statistics also exposed systemic inefficiencies within the CPS, which took 41,000 cases to court then dropped them at the last moment when lawyers offered no evidence.

Conviction rates reflect other factors including the social composition of juries in different crown courts and the contrasting nature of crime in different parts of the country.

But the performance figures coincide with growing concern about courtroom prosecution.

HMCPS Inspectorate will begin grading the 42 CPS areas next month as excellent, good, fair or poor. The Times has also learnt that Avon & Somerset Constabulary is conducting its own audit of CPS performance in the Bristol area.

Ken Macdonald, QC, Director of Public Prosecutions, defended his service’s record. “Do you want to live in a country where the national conviction rate is 98 per cent or 100 per cent? There are such countries and our people generally don’t want to live there,” he said.

“If the national conviction rate is 82 per cent, which is up by 3 per cent over the last couple of years, I think that is pretty good. There’s not such a huge spread between the highest and the lowest. One can always improve and obviously we want as much national consistency as possible, but we are dealing here with judges and magistrates — criminal justice is driven by human beings, it is not scientific practice.”

Mr Macdonald said that different levels of performance could be explained in part by contrasts between shire counties and metropolitan areas and in different practices. He said that where prosecutors had taken over the task of charging from police officers, performance was improving.

But he expressed concern over the low rate of conviction for sexual offences and the collapse of so many cases.

Ian Kelcey, chairman of the Criminal Law Solicitors Association, said that defence lawyers were increasingly frustrated by CPS delays.

Mr Kelcey said: “You can write letters for months and never receive a reply, and there are huge differences in levels of efficiency . . . Every delay hampers the smooth running of the justice system.”