London has 10,000 crime-fighting CCTV cameras which cost £200 million, figures show today.
But an analysis of the publicly funded spy network, which is owned and controlled by local authorities and Transport for London, has cast doubt on its ability to help solve crime.
A comparison of the number of cameras in each London borough with the proportion of crimes solved there found that police are no more likely to catch offenders in areas with hundreds of cameras than in those with hardly any.
In fact, four out of five of the boroughs with the most cameras have a record of solving crime that is below average.
The figures were obtained by the Liberal Democrats on the London Assembly using the Freedom of Information Act.
Dee Doocey, the Lib-Dems' policing spokeswoman, said: "These figures suggest there is no link between a high number of CCTV cameras and a better crime clear-up rate.
"We have estimated that CCTV cameras have cost the taxpayer in the region of £200million in the last 10 years but it's not entirely clear if some of that money would not have been better spent on police officers.
"Although CCTV has its place, it is not the only solution in preventing or detecting crime.
"Too often calls for CCTV cameras come as a knee-jerk reaction. It is time we engaged in an open debate about the role of cameras in London today."
The figures show:
• There are now 10,524 CCTV cameras in 32 London boroughs funded with Home Office grants totalling about £200million.
• Hackney has the most cameras - 1,484 - and has a better-than-average clearup rate of 22.2 per cent.
• Wandsworth has 993 cameras, Tower Hamlets, 824, Greenwich, 747 and Lewisham 730, but police in all four boroughs fail to reach the average 21 per cent crime clear-up rate for London.
• By contrast, boroughs such as Kensington and Chelsea, Sutton and Waltham Forest have fewer than 100 cameras each yet they still have clear-up rates of around 20 per cent.
• Police in Sutton have one of the highest clear-ups with 25 per cent.
• Brent police have the highest clear-up rate, with 25.9 per cent of crimes solved in 2006-07, even though the borough has only 164 cameras.
The figures appear to confirm earlier studies which have thrown doubt on the effectiveness of CCTV cameras.
A report by the criminal justice charity Nacro in 2002 concluded that the money spent on cameras would be better used on street lighting, which has been shown to cut crime by up to 20 per cent.
Scotland Yard is trying to improve its track record on the use of CCTV and has set up a special unit which collects and circulates CCTV images of criminals.
A pilot project is running in Southwark and Lambeth and is expected to be rolled out across the capital.
The figures only include state-funded cameras.
The true number, once privately run units and CCTV at rail and London Underground stations are taken into account, will be significantly higher.