By Caroline McClatchey
John Smeaton is one of the best known have-a-go heroes of recent times
When it comes to members of the public intervening to stop crime, the police message, more often than not, has been to step away and call 999.
But now the UK's top police officer, Met Police Commissioner Sir Paul Stephenson, has said people should be encouraged to tackle criminals.
"I do get worried on occasion that we get our advice wrong," he said.
"People have got to make a reasonable judgment but to actively discourage them from being responsible citizens is wrong."
The police "line" on whether or not people should step in or away has never been crystal clear.
Forces are reluctant to come down on either side for fear of being accused of promoting vigilantism or condemned for their comments when a member of the public is killed trying to prevent a crime.
So-called have-a-go heroes generally only make the headlines when the story has a tragic ending or it is extremely newsworthy.
One of the best known of recent times is John Smeaton, the baggage handler who became a national figure following the bomb attacks on Glasgow airport in 2007.
He helped police tackle a man who drove a jeep into Glasgow's terminal building.
And the most recent tragic tale is that of 31-year-old Sukhwinder Singh, who was stabbed to death after chasing muggers who had snatched a woman's handbag in east London on 8 January.
John O'Connor, a former commander of the Flying Squad, told the BBC the police had "backed away" from encouraging people to intervene in the 1960s.
He said Sir Ranulph Bacon, then deputy commissioner at New Scotland Yard, had urged the public to "have a go" at criminals. The complete slogan was "If you have a chance, have a go".
Sir Paul Stephenson said have-a-go heroes made our society worthwhile
He was accused of being irresponsible and Mr O'Connor said it all changed when someone was killed.
While the police continued to praise, support and award bravery medals to have-a-go heroes, he said, there had been a reluctance to urge people to take action.
"In an increasingly violent society there is more likelihood that members of the public who intervene will be shot or maimed," he said.
He believes that by speaking out, Sir Paul is trying to re-connect with the public and get them back on side.
"The public is not supporting the police," he said. "The police cannot do their job without the wider support of the public - whether intervening when they think they are capable or more importantly coming forward as witnesses."
In England and Wales, anyone can use "reasonable" force to protect themselves or others, or to carry out an arrest or to prevent crime.
The Conservatives' message on this is clear - they would like to make it easier for the public to stop anti-social behaviour and crime by reducing the risk that have-a-go-heroes will find themselves being prosecuted.
They also want to amend the law in favour of the householder to give them certainty that they will not be prosecuted if they attack an intruder.
Justice Secretary Jack Straw has been able to draw on personal experience when it comes to have-a-go heroes.
Over the years his exploits have included chasing (and catching) a burglar in his Blackburn constituency and rescuing a mugging victim at Oval Tube station in London - he chased her attacker for more than half a mile.
He ordered a review in 2007 to clarify "that the law is on the side of the citizen", but he was criticised for doing no more than restating the existing legal position.
"As long as they use no more force than necessary, people should have confidence that the law will support them," said a Home Office spokesman.
"Dealing with crime is not just the responsibility of the police, courts and prisons; it's the responsibility of all of us. Communities with the lowest crime and the greatest safety are the ones with the most active citizens."
Professor Gloria Laycock is an expert in crime prevention and worked in the Home Office for more than 30 years.
A 2006 survey, which she worked on, suggested the British were the least likely in Europe to intervene in crime.
The poll indicated six out of 10 Britons would be unlikely to challenge a group of 14-year-old boys vandalising a bus shelter, more than Germany, the Netherlands, Italy, France and Spain.
Prof Laycock said she did not think there was a police message on intervention never mind a consistent one.
"Sir Paul is probably one of the first to step up," she said.
"I think he is trying to start a debate. We need debate about where the boundaries are, what it is ok to do, and what the police will thank you for doing rather than arrest you for doing."
She thinks the debate should focus on anti-social behaviour, adding many adults are wary of getting involved in case they are accused of assault.
'Walk on by'
Recent official statistics suggest 55% of people think the police are doing a good job but only about 40% believe the criminal justice system as a whole is effective.
Guy Dehn, head of the charity Witness Confident, said people had forgotten that the police were established as "citizens in uniform" and the public's civic duties have "almost ceased to exist".
He said Sir Paul's comments were a welcome "shift" and it was time to take a stand against the "walk on by" culture.
Sukhwinder Singh was stabbed to death as he chased muggers
"We welcome the fact the police are now breaking with their recent record of discouraging people from being good citizens," he said.
While the charity does not generally advocate physically tackling the criminal, Mr Dehn said doing nothing was a "mugger's charter".
There were a few things people could do without jeopardising their own safety, he said, such as shouting and screaming, taking pictures of the assailant on a mobile phone and calling for other people to help.
Sir Paul's comments on Wednesday have been confusingly linked to the case of Munir Hussain, who was freed the same day by the Court of Appeal.
The 53-year-old millionaire businessman was jailed for permanently injuring an intruder who attacked him and his family but his sentence was reduced and suspended.
Although the judgement had more to do with the unique facts of the case rather than the law of self defence it has re-opened the debate about what is considered "reasonable force" and the rights of the victim versus the perpetrator.