Would you risk your own life to help a stranger in danger?

A recent report found that British people are the least likely of all Europeans to step in if they witness a crime. But would you intervene to assist a stranger in danger?

The fight happened 14 years ago, when Heidi Scrimgeour had just turned 18, but it is still one of her most vivid memories. Walking home late one night with a male friend, she turned a corner and saw two men beating someone up. "They punched him in the head until he fell to the ground, and then they took it in turns to kick him in the head," she says. "I vividly remember watching his head bounce on the pavement, exactly like a football, and a surreal sense of being surprised that heads did that." In shock, Scrimgeour stayed rooted to the spot, watching, until her friend – adamant that it was too dangerous to get involved – pulled her away. "It was like watching a scene in a film and although every kick made me wince at the thought of the pain, I still couldn't process the brutality. I'd never seen violence like that." She heard later that the victim was in intensive care and possibly suffering brain damage. "I still feel sick at the thought of that. The idea that someone might just walk past one of my children during an attack doesn't bear thinking about." Scrimgeour is honest, though, about her personal expectations if she came across a similar incident: "I still feel a bit ashamed that I didn't at least make an effort to intervene, but I can't honestly say I'd do anything different. In an ideal world I'd leap to the defence of the person being attacked and save the day – but that's not real life."

The official advice is not to intervene – and as a new Cutting Edge documentary for Channel 4 shows (see case studies, overleaf), the perils of getting involved can be great. The Metropolitan Police, while keen not to undermine the bravery of so-called "have-a-go heroes", counsels people to dial 999 rather than approach a violent scene. The fear of knife crime, too, is a strong deterrent to action, and one reinforced from the highest levels. Boris Johnson's advice in 2007 to "take a risk" was subject to an abrupt about-turn a year later, in the wake of the Met's crackdown on knives: "Whatever you do, if you see a fight in the street, don't risk it because someone could have a knife," the Mayor of London advised in July last year.

Yet some situations demand a risk. Two years ago, Mark Reid – aged 25 at the time – had just parted ways with two friends after an evening together. His friends went to wait for a bus on London's Tottenham Court Road, when they were cornered and attacked by two men. Reid ran back, and told the men to leave them alone. "One of them grabbed me by the neck and the other punched me," he says. "I punched the guy holding me by the neck, and when he fell to the ground, we started walking away." But the incident was far from over. "One of the men ran towards me carrying a roadside bin over his head. There were lots of people around – over 50 – who saw him throw the bin at me," Reid says. "As I dodged it, I tripped over myself. He jumped on top of me, pinned my shoulders against the ground and sunk his teeth into my lip." Reid begged him to stop, but the man bit further, taking 3cm – including the muscles of the corner of his mouth – out of his face. "I heard screams from people who were watching but no one came to help. He spat the lip out next to me, and ran off, his face covered in my blood." Over the coming months Reid underwent five operations of reconstructive surgery, yet despite the trauma, he is sanguine about the reaction of the witnesses. "My attacker was screaming, wildly aggressive – it's understandable that a stranger wouldn't intervene."

Professor Helen Cowie, a fellow of the British Psychological Society, is a specialist in "bystander apathy", and believes that passivity is not simply a modern malaise. "Sometimes people think that this is a new phenomenon," she says, "but this is not the case. We need to understand the social dynamics of a situation in order to understand the circumstances in which people show reluctance to help others." The number of bystanders, for instance, matters. "When people are alone, they are more likely to take action but when the group remains inactive the percentage of people who will take action plummets." In experiments in which people witness an attack (by actors on actors, though the subjects of the experiment don't know this), the interviews afterwards show that within a group, people are inhibited from taking action if no one else does. "They feel embarrassed about standing out," Cowie says. "They also are more likely to minimise the danger when they see that no one else is taking action." On top of this, she says, the more people present at an emergency, the greater the diffusion of responsibility. "People decide that there must be someone else more qualified than they are to take responsibility for intervening to help. If someone is a friend of the victim, they are much more likely to intervene."

Two months ago, Sophie Richards was in one of four cars sitting at traffic lights in north London, when she and her boyfriend witnessed a teenage boy being attacked by a group of teenagers. "The whole group was attacking him, punching and kicking him in the head. I was amazed at how violent they were," she says. "I was screaming, and shouting at my boyfriend to do something – it looked like they were going to kill him." Concerned about knives, her boyfriend called the police, and kept his hand on the car horn, to alert the gang that people were watching. It worked, and they ran off, but not before they'd inflicted damage. "The kid was fitting on the ground – he'd had a sustained kicking to his head," Richards says. "The first car drove away, which the police said was a pity because they saw everything and could have provided a statement, but the others stayed to help." Her boyfriend said later that he thought if he'd got out of the car others would have followed – and indeed, he would have jumped out if others had first. "He said honestly that he wanted to, and that if it was someone he knew he'd be out like a shot, but he didn't want to be stabbed for someone he didn't know."

For Sarah Wilkinson, being attacked in the vicinity of passers-by was no help. Waiting for a bus with a friend at Wakefield station last December, the 19-year-old was approached by three girls who asked her for a cigarette. When Wilkinson refused, they became increasingly hostile. "They were shouting at us and giving dirty looks," Wilkinson says, "and then one of them punched me in the eye, pushed my head back into the glass window, and put a cigarette out in my face." It was mid-afternoon and there were people walking in and out of the station, but despite the commotion nobody came over. "Quite a few people were looking but no one did anything," she says. "It went on for 10 or 15 minutes. We tried to get on the bus but they stopped us. My friend was crying her eyes out but they said if we shouted for help, they'd punch us again." The ordeal only ended when the attackers left. "I thought someone would help, but they kept looking and walking off. It's changed my opinion of people," Wilkinson says.

However contrary to human instinct the reactions of those passers-by to Wilkinson's plight seem, they do not counteract research on this subject by the think-tank Reform. The Lawful Society report, published last September, found that British people are the least likely of all Europeans to step in if they witness a crime, with the archetypal "Have-a-go hero" more likely transformed into a "passive bystander". Three-quarters of Britons – as opposed to 45 per cent of French or Germans – think it's the responsibility of the police and courts to confront anti-social behaviour. The idea that intervention is an individual's responsibility seems to be falling away in the UK. Perhaps that is because tackling anti-social behaviour can come at a price. Matt Cross was travelling in a packed carriage on the London Underground with another passenger who was playing his music on loudspeaker through his phone. "It was making everyone feel uncomfortable and the journey a little bit worse," he says. "It was so loud, it got to point where I said, 'Can you turn that up a bit?' Somebody laughed: everyone was thinking exactly same thing. Somehow I thought he'd say, 'Oh, I'm so embarrassed, sorry, I forgot my earphones'." Instead, the man stood up and became verbally confrontational. "He was spouting off like a rapper. I stopped speaking, but he kept going." After unsuccessfully challenging Cross to get off the train, the man punched him in the face. "When he left the train, everyone said well done to me – then everyone spoke." The punch left Cross with a broken cheekbone, and a steep learning curve. "It was a great lesson – if you speak to someone, you're welcoming them in. There's bound to be an altercation. I think being sarcastic embarrassed him, and he had nowhere to go but defend himself."

For Professor Cowie, the technique of intervention is key: "It's pointless to put yourself in danger needlessly, but there are many ways to help a person in distress. I once saw a man was violently threatening his wife. A crowd surrounded him silently but intently. After a few minutes he stopped shouting and left the scene." To stop and help someone, or challenge behaviour you find unacceptable, requires a split-second decision: perhaps it's a decision you need to take theoretically before you're confronted with it. Would you risk your life to help a stranger?

Some names have been changed. 'Cutting Edge: Would You Save a Stranger?' is showing on Channel 4 on 2 April at 9pm

Steve Kendrick confronted two thieves robbing a corner shop

It was November 2005, and I stopped off at a shop in Shropshire at about 8.30pm on a Saturday. I was the only customer. Somebody appeared in the doorway, wearing a mask. Another guy came in after him, wearing a mask and gloves, and holding a pistol. He shouted to the girls behind the till to open the safe. The women had a look of sheer terror: I had to think quickly. I told the men to cut their losses – the girls were Saturday staff and couldn't open the safe. He went ballistic, waving the gun in my face; it went off but missed. He lunged at me and smashed me on the lip with the barrel. He went to reload, so I tried to wrestle it off him, but he had a knife in his other hand. He left an inch-and-a-half-long hole in my elbow and a three-inch hole in my shoulder. He slashed my neck but luckily my backbone stopped it, and then he cut across my ribs, and slashed my stomach open and wiggled the knife about. He realised he'd done enough to stop me and ran off. When they'd gone, the girls called 999 and I phoned my girlfriend who was a nurse. Blood was pouring out of me; a bit of my stomach was hanging out. When my girlfriend arrived she hugged me: in that situation you need human contact. I think I would have faded away if she hadn't done that. I had major stomach surgery, but it wouldn't stop me helping someone in the future.

Jasmine Kranat was attacked on a bus by a gang of teenage girls

When I was 12, my friend and I were on a bus from Colindale [north London]. Some girls boxed us in at the back and asked for chewing gum; my friend gave her a packet and they finished it. They asked for a pound – we'd spent all our money, but they searched me. People were sitting all round, but no one gave me eye contact. I shouted, "Please let us off the bus!" but no one did anything. It was a single-deck bus, and I'm sure everyone heard. One of the girls punched me in the face. I fell backwards. Next I was on the floor and she was jumping from the bus seats on to my face and chest, and I was screaming. Someone in the girls' group said that was enough, so she stopped. When I got up, she tried to grab my phone and was pulling my hair. I was in the aisle and everyone was looking: I was battered in the face, my chest was bleeding, and she was screaming, "Get her phone". I squirmed away, screaming for the driver to let me off, which he did like nothing had happened. I had a fractured eye socket, bruised chest, black eye, massive bumps on my head and forehead, and half my hair fell out. My face was double its normal size.

If one of those people had said something it could have changed everything: I wouldn't have had to switch schools. People would expect you to help their daughter, but they wouldn't help me.

Howard turner intervened to help a stranger in distress

About three years ago my partner Geraldine and I were walking back from a concert and dinner near Waterloo. It was about 11.30pm, and there was bit of a fracas going on across the road. Nothing huge: a chap, who we later learnt was called Peter, was walking along, and two blokes behind him were giving him a bit of verbal hassle. Then one of them, who was wearing a suit, threw a punch at Peter, and he went down like a bag of spanners. The aggressor just laid into him like crazy, kicking his head like a football – it looked awful. It's not like me, but I lost my rag: I think without Geraldine there physically holding me back, I would have steamed in. It was a blatant violent assault for no reason, and it lit my fuse. Neither of our phones were working, but I was shouting that I was going to phone the police, which seemed to break the moment. He shouted I'd be next, and stopped kicking Peter and began to walk over to me. His friend walked on a bit, and then the guy in the suit sauntered off too, hands in pockets. We went over, and Peter was bleeding, with a massive swelling on his forehead. I thought he was going to die. We used his phone to call the ambulance. My response was primal. I don't feel courageous, I feel selfish: I wouldn't want that happening to me. How awful if he was lying there in a pool of blood, and we hadn't helped.