When Gloria Taylor collapsed in the street near her south London home last week, the medics said she’d had a heart attack. Those who knew her disagreed; they said she had died of a broken heart.

Damilola Taylor, her 10-year-old son, also died nearby in Peckham eight years ago after he was stabbed. Damilola’s death was a big event. There was an outpouring of grief at how a young boy who had come from Nigeria to find a better life had ended up bleeding to death alone in a grim stairwell on a wretched council estate.

At the time I was the Focus editor on this paper and we dispatched a reporting team to Nigeria to find out where Damilola had come from and pieced together, forensically, his life and times. The story ran and ran. The footage of him leaving the library in Peckham on his fateful journey home, his cheeky grin, his bag of books, became almost as iconic as the film of James Bulger being led out of the shopping centre by his killers. It was shocking that such a thing could happen to such a young, innocent boy. It seemed a violation of the social fabric.

How different things are now. Already this year (and it is only April) there have been 11 murders of young people (predominantly from ethnic minorities) in London. Last week two particularly grisly murder cases concluded at the Old Bailey. The first was the chilling tale of how Kodjo Yenga, 16, was set upon by the MDP gang (it stands for Murder Dem Pussies) in broad daylight in a well-to-do area of Hammersmith in west London. A group of boys with knives, hammers and baseball bats beat and stabbed him, shouting, “Catch him! Kill him!” Church-going Yenga was studying for his A-levels.

The second case that the Old Bailey heard was that of the death of Paul Erhahon, who was walking home in Leytonstone, east London, when he bumped into the Cathall Street Bois gang. One of the older boys ordered the younger members of the gang to attack him: Erhahon was stabbed in the heart with a sword in what seemed to be a kind of initiation into what the judge termed the gang’s “cult of violence”.

According to a recent poll, a third of 13 to 18-year-olds in five London boroughs know someone who has been stabbed. This newspaper recently revealed the tragic tale of a young girl who had had seven friends either shot or stabbed to death. This is not just a London phenomenon - Rhys Jones, 11, was shot in Liverpool as he walked home from football. Sophie Lancaster, the goth girl who tried to stop a gang killing her boyfriend, was stamped to death in Bacup, Lancashire. Gang violence in Manchester and shootings in Nottingham are legion.

At least when Damilola died there was shock. Now there seems to be a grudging acceptance of the increased violence. It has become depressingly normal - and we have adjusted our behaviour accordingly. David Cameron may encourage us to “be responsible”, to tell off yoofs who are behaving badly, to be model citizens and reclaim the streets. Well, while I agree with you in theory, in practice it’s more than your life is worth.

At half-term I was on a bus with my five-year-old daughter. She had wanted to see Buckingham Palace, so we saluted the Queen and walked back up The Mall to get a bus home from Trafalgar Square. The bus was packed, around us were a friendly posse of young people of all races, bantering, cracking jokes, smiling. I felt happy - when the capital’s mad melting pot works, it’s great.

Suddenly there was a kerfuffle among the packed-in bodies by the doors. From the shouts, it seemed that a middle-aged white guy had stepped on a young black man’s foot. The bus stopped and as the doors opened, the young guy started punching the older man in the head. He wrestled him off the bus, kicked him to the ground and left him there. Calmly he got back on the bus.

Silence fell. My daughter looked at me anxiously. I hugged her and whispered not to worry, but when I looked up I inadvertently caught the thug’s eye. “What you f****** looking at?” he yelled. I cast my eyes down quickly, glad that there were many bodies rammed in between me and him. No one moved, said or did anything. We all tried, desperately, to mind our own business. The bus continued on. About three stops later he got off. The chatter resumed as if nothing had happened.

I don’t think that bus was full of cowards. We were just realists. We read the papers, we know the story about the man who got stabbed on a bus for asking a young guy to stop throwing chips at his girlfriend. The reality of the level of violence among a particular subsection of society is such that sometimes it’s just not safe to intervene any more. I didn’t want to be a hero if death could be the consequence. I just wanted to get home from a day out with my daughter with both of us in one piece. Like everyone else on that bus.

Afterwards I felt ashamed and found myself murmuring, “All it takes for evil to triumph is for good men to do nothing.” Ouch. I felt sad that there was no brave man on the bus ready to tackle this guy in the name of civilised values. I thought about calling the police - but by then it was too late (and they probably wouldn’t have done anything anyway). But, perhaps most depressingly, I didn’t feel shocked or surprised by what I’d seen and nor did anyone else. It is too common.

I have talked to numerous experts about what makes young men like this so violent. Most blame an escalating cycle of fear. Kids feel scared because they live on bleak, violent estates, so they carry knives. Then if they feel threatened they use them. Then it becomes not enough of a deterrent to have just a knife, so the hard-nuts get pit bull dogs or guns. Then any fracas has the potential to escalate into a life-threatening situation. The more kids who get killed, the more acceptable death becomes, the more frightened the rest feel and the more inured to violence these young men become. So the cycle continues.

Camila Batmanghelidjh of Kids Company, who arguably knows more about this - and does more to help kids stuck in this cycle - than anyone, says that the youths we are most scared of are probably those who are the most scared themselves. And so the normal scuffles and braggadocio of youth become a deadly cancer to the whole of society.

Boris Johnson says that if he becomes mayor of London he is determined to tackle the violence: he wants conductors back on buses (who might have intervened on my bus, I suppose) and says he’ll take free travel away from teenagers who abuse that right. That’s all a step in the right direction - but it’s not going to put the genie back in the bottle.

In New York, through tough, plentiful policing, Rudy Giuliani reclaimed the subway and public spaces for ordinary people. Boris, can you do that for London?

India Knight is away

Times Recommends

• We have kit and leadership. Let’s go
• Behind the scenes at the biggest deal
• Conferences — what a waste of money