Sir Paul Stephenson said the police should be grateful that people act
People who put themselves in danger to tackle criminals should be celebrated as heroes, the UK's most senior police officer has said.
Metropolitan Police Commissioner Sir Paul Stephenson said such people "make our society worthwhile".
Police should encourage people to intervene, not just allow them to do so, the commissioner added.
London has recently seen three cases in which people have died after intervening in violent situations.
'Bravery and courage'
Speaking at New Scotland Yard, Sir Paul said: "I have worried on occasions that we have got the advice slightly wrong.
"I am not saying to people 'You should feel guilty about not tackling this 18-stone monster'.
"People have to make reasonable judgments, but actively discouraging people from being active citizens seems to me to be wrong.
"Our first response should not be to discourage people from doing it. It should be to applaud their bravery and courage.
"Our first response should be to express gratitude that we have got citizens who would do that thing."
Three people have been killed in London recently after acting in the face of violent situations.
• Sukhwinder Singh, 31, was stabbed to death after chasing muggers who had snatched a 28-year-old woman's handbag in Barking, east London, on 8 January.
• Frazer Bradshaw, 33, suffered fatal head injuries as he tried to break up a brawl outside a pub in Uxbridge, west London, in the early hours of New Year's Day.
• David Joslin, 23, was fatally injured trying to break up a fight between two groups as he walked past them in Chingford, east London, on 20 December.
Sir Paul said: "We ought to be saying to relatives 'these people are heroes. These are people who make our society worthwhile'."
The commissioner, who said his wife once intervened several years ago when a woman was being abused on a London bus, said he did not want people to have the added burden of waiting to find out if they were going to be prosecuted.
"How do we at the sharp end, the cops, the CPS, put people out of their misery of worrying about these things?" he said.
Three men have been killed while intervening in recent weeks
"Because in the vast majority of occasions people do not have to worry about these things.
"People should not have to worry about making the proper actions, common sense actions, of things we would all support."
Sir Paul's comments came on the day Munir Hussain, who was jailed for permanently injuring an intruder who attacked him and his family, was freed by the Court of Appeal.
Hussain, 53, of High Wycombe, Buckinghamshire, had been sentenced 30 months for grievous bodily harm with intent but that was reduced to 12 months suspended for two years.