The Times obtained the data through a freedom of information request which led to the disclosure of spreadsheets of monthly case outcomes.

Further study of the results was carried out with the help of the Danish International Center for Analytical Reporting (DICAR).The figures, covering just under a year’s caseload between September 2004 and August 2005, were refined to identify trends in performance by the CPS’s area offices and national patterns in the handling of different types of offence.

The CPS and its independent inspectorate has no plans to draw up similar league tables although the 42 areas are soon to be graded as excellent, good, fair or poor.

Tables, it says, are misleading because they lead to unhelpful comparisons between very different areas, such as West Mercia and Greater Manchester.

There are pitfalls. Factors such as the social composition of juries at different courts and the differences between rural and city crime have a huge influence on conviction rates.

But the data can be fairly used to identify regional offices which perform consistently poorly across the range of offences and to pinpoint types of crime where prosecutors across the country are struggling to secure convictions.

BEST & WORST

The best performing CPS area office, according to conviction rates, is Warwickshire, which is successful in 93 per of the cases it handles. The regional office has high conviction rates across the whole range of cases from homicide (where it secured 12 convictions in 12 cases) to motoring.

But Warwickshire’s apparent success is skewed by the high level of motoring offences which returned a 96 per cent conviction rate.

Bedfordshire always appears at or close to the bottom of the performance tables. Of 1,590 cases of offences against the person, only 51 per cent resulted in convictions. The CPS inspectorate found in June 2004 that Bedfordshire had fewer lawyers than in 2001 and that the workload handled by each prosecutor had risen from 695 cases per year to 875.

Criminal lawyers also point out important demographical differences. Warwick Crown Court is noted for having “stockbroker belt” juries and high conviction rates. Bedfordshire includes the high-crime town of Luton.

HOMICIDE

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