The figures also suggest that increasing numbers of forces have relied on keeping clear-up rates high by including crimes convicted criminals say they have committed.
Tony Blair, Labour's home affairs spokesman, said that the latest figures were alarming: 'It is essential that the Home Office responds to criticisms of crime statistics and puts them on a proper and verifiable basis. There is no other way of restoring confidence in the system.'
On Wednesday, the Independent disclosed that a growing number of forces were reporting unprecedented slumps in overall detection rates for 1992, continuing a trend that began when crimes started to rise dramatically three years ago.
Responding to the report, Kenneth Clarke, the Home Secretary, said better statistics, based on the Audit Commission performance indicators, were needed before 'laggard' forces could be improved.
One indicator is 'primary' clear-ups - where the police charge, summon or caution an offender for specific crimes following investigations.
These are different from 'secondary' clear-ups obtained from convicted prisoners, who ask for them to be taken into consideration at trial or admit to them at 'prison visits'. The secondary clear-ups are considered notoriously unreliable. A breakdown of these figures for 1989, 1990 and 1991, the first years they have been collected, shows wide variations, with Gwent topping the league table by actually solving 39 per cent of recorded crimes, and the Metropolitan Police coming last with 12 per cent.
The best 10 forces all serve country areas, the bottom 10 are largely metropolitan. Almost half the forces have primary clear-up rates below 20 per cent. In 1991, the official clear-up rates for Gloucestershire, Merseyside and Greater Manchester contained more secondary clear-ups than charges or cautions.
The number of forces using prison visits to account for substantial proportions of clear-up rates has risen over the three years up to 1992.
On Wednesday, Mr Clarke criticised forces 'wasting police officers' time by sending them round the prisons to clear up the books. (It) makes the figures look better but doesn't actually do what the public wants.'
In 1989, eight forces relied on prison visits for 20 per cent or more of their clear-ups; in 1991, a total of 12 forces did so. With the percentage of the clear-ups accounted for by prison visits in brackets the forces are: Dorset (28); Gloucestershire (32); Greater Manchester (32); Lancashire (22); Merseyside (40); Norfolk (20); Northumbria (25); South Yorkshire (24); Staffordshire (23); West Midlands (25); Dyfed-Powys (20); and South Wales (34).
The practice is permitted under strict guidelines but a number of forces, including Cheshire and Northumbria, have recently abandoned it.
David Shattock, Chief Constable of Avon and Somerset, where the overall detection rate plunged from 33 per cent in 1989 to 17 per cent in 1992, said the low rate was because his force had targeted for the first time 'criminals and not crime'.
Cumbria police said last night that the targeting of suspects over the past fortnight had led to 69 arrests, the clearing up of more than 600 crimes and recovery of thousands of pounds of stolen goods.
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