The guardian ran a piece on CCTV back in 2008 referencing a report on a government website that basically stated CCTV isn't that effectivehttp://www.guardian.co.uk/technology/2008/jun/26/politics.ukcrime
The report seems to have mysteriously disappeared from the government site though
if anyone can find it or has a copy I'd be grateful for a link, the original link was http://www.homeoffice.gov.uk/rds/pdfs05/hors292.pdf
and the conclusion which I'd quoted on another site went as follows
Research on the effectiveness of CCTV has painted a somewhat confusing picture. There are plenty of studies showing successes, but plenty highlighting failures too. The most robust studies, according to the criteria deemed acceptable according to the Campbell Collaboration, compound the confusion. While CCTV in some locations, and car parks are the best example, show some success, it is typically introduced alongside other measures. No single study appears to have included a process and impact evaluation taking account of the various objectives and seeking to develop transferable lessons for good practise. More over, residential areas have received scant coverage and there is little knowledge about whether CCTV works there.
Though without the original to check against this is just hearsay
.... AH I found the report http://webarchive.nationalarchives.gov.uk/20110220105210/rds.homeoffice.gov.uk/rds/pdfs05/hors292.pdf
that conclusion was at the top of page 9