Almost 11,500 fewer citizen's arrests were made in London in 2010 than in 2002, figures have revealed, as experts point to a rise in "fear of crime".
The Metropolitan Police said that 14,047 citizen's arrests were made in 2002, but by 2010 that number had fallen to just 2,579.
The figures, released after a request by the Daily Telegraph under the Freedom of Information Act, also showed that the number is expected to fall below 2,000 in 2011.
By 2006 the number had fallen to 6,306, and as of July 2011 had dropped as low as 1,164.
'Citizen's arrest' was defined in the figures as somebody 'given into custody', meaning the police were handed control of a suspect by somebody who did not have the power of arrest, including members of the public, Police Community Support Officers (PCSOs) and private security forces.
Scotland Yard identified no specific causes for the decline, but the figures are surprising in part because PCSOs were introduced in 2002, and their presence might have been expected to increase the number of citizen arrests.
Commenting on the numbers, Jon Collins, deputy director of the Police Foundation, a policing think tank, said:
“These figures do not in themselves provide an explanation for the significant drop in the number of citizens arrests conducted in London, and without further research any speculation as to its causes is likely to be inconclusive.
"More research on what has caused the reduced number of citizens arrests would therefore be interesting and useful, as it is important for members of the public to feel confident in intervening to prevent a crime taking place or to apprehend an offender, where it is safe and appropriate."
"The public has an important role to play in tackling crime. However this goes much further than making citizens arrests. It is also important for the public to provide the police with the information and intelligence that is essential for successful policing.”
Reports cited changes in the law designed to more strictly define the boundaries of legal citizen's arrest as one possible cause for the decline.
In 2006 it was declared that intervention by the public was only allowed in serious cases. The law was also changed to ensure that an arrest could only be legally made if no police officers were available, and if the person making the arrest was sure it was necessary to prevent injury or serious damage to property.
The Crown Prosecution Service has also warned that the use of force in a citizen's arrest could be classed as illegal assault.
Cases of citizen's arrest gone awry are not hard to find: in 2008 a man who said he made a citizen arrest against a vandal smashing a shop window was accused of assault and arrested.
In a 2006 report by security company ADT and UCL it was revealed that British people were less likely than people in Western Europe to intervene in low-level crime.
Around 62% of Britons said they would not intervene in that online study, compared to 48% across Western Europe as a whole.
Ben Rogers, director of the Demos Centre For London, told the Huffington Post UK that the figures "had to be taken at face value" but suggested that changes in reporting practice might partly explain the fall. Even so, Rogers said, that would usually result in a sudden drop and not the "steady decline" seen over the past decade at a time when crime, and fear of crime, was falling on average.
Rogers wrote in a 2010 essay quoted the ADT report and argued that the declining presence of 'local authority figures' including park keepers, milkmen and postal workers was one possible cause of the decline.
He also said that narrow performance targets in those roles had made its workforce less willing to intervene, and added that social ties had loosened as a result of "greater diversity and churn" in local communities.
There has also been "a rise in the perception that the system is weighed against people who ‘take a stand’ and in favour of ‘offenders’, with the former too often subject to official criticism or prosecution", Rogers argued, as fear of crime has risen.
"We are, in short, more fearful than we were that any intervention could result in us, our families or communities being attacked or otherwise victimised," he said.
In America, at least, it appears citizen's arrest is alive and well: actress Lindsay Lohan apparently made one such arrest over the weekend after a man was caught trespassing in her home.