The Evening Standard's website, This Is London, reports that:
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.It's all a bit meaningless, though. There's no consideration of the effects of installing (or removing) cameras; if a high crime area has a lot of cameras, this is taken as a sign of failure where it might just be a sign that cameras have been concentrated where the crime is worst.
In fact, four out of five of the boroughs with the most cameras have a record of solving crime that is below average.
I suspect what happens is an immediate improvement or displacement of crime, followed by a gradual return to the status quo ante as people get used to the cameras and develop counter measures (like hoodies).
I used to sell CCTV equipment, and one day in the late 1980s spent a morning with the security manager of King's College Hospital in London. There was a scramble to install CCTV after a baby had been abducted from another hospital a few months earlier, in a case that made headlines. As we walked around the site, the manager said he'd show me something, and led me to an old air raid shelter that had been converted into storage.
He unlocked the door, and showed me shelf after shelf of boxed colour CCTV cameras. I think he said they had cost £16,000 a couple of years earlier. Two different committees, in two different agencies, had shared budgetary responsibility for security. The one that could decided to buy the cameras. The other committee held the purse strings for installation, but because of rivalries they were piqued that the first committee had bought the cameras and refused to allocate any money for installation. The cameras had sat in storage ever since.
Now, because of the structure of the procurement process, it was easier to buy new cameras than to get the ones they already had installed. The security manager shrugged, locked the air raid shelter, and asked me to include cameras and installation in the new quote.