Police are alerted to fights more quickly via CCTV

Scientists at the University Hospital of Wales found there was no evidence of any prevention of violence when town centres were monitored.

However, the presence of security cameras did help reduce the severity of injuries inflicted in street fights.

They also alerted the police to trouble more quickly and reduced the number of people needing emergency hospital treatment, the research published on Monday in the journal Injury Prevention showed.

The report stated: "The benefit of CCTV might lie less in preventing such offences ... but more in facilitating a faster police response to arguments or assaults in public spaces, which limits their duration and therefore reduces the incidence and seriousness of injury."

The research has highlighted inadequacy and "inappropriateness" of official police statistics on violent crime which showed only a quarter of assaults leading to treatment in casualty departments.

True measures have got to take into account injury data from local hospitals as well as police information. Professor Jonathan Shepherd

The report claims to be the first to compare police and hospital data, and authors said its four-year time span was longer than other CCTV studies.

The research studied reports from police between 1995 and 1999 covering street violence in five towns with cameras put in place, and five towns without CCTV, and checked it against casualty records for assaults treated.

Detection rates by the police of street assaults remained the same - the authors said they would have fallen in the towns with CCTV cameras if they were acting as a deterrent.

Co-author Professor Jonathan Shepherd, professor of oral and maxillofacial surgery, said: "The benefits of CCTV probably include enabling the police to get to a punch-up or brawl earlier than they would otherwise.

"The evidence shows you can't rely on police violence statistics as an accurate measure of violence in the community.

"True measures have got to take into account injury data from local hospitals as well as police information.

"About a quarter of assaults which lead to A&E treatment appear in police lists and official crime statistics."