The baby, unbothered by diesel fumes, enjoys an outing down the main road through London N1. Each passing bus is marked by a fat and pointing finger: ‘There!’ On the way to our local park last Thursday, we had just begun to cross the road, pointing up at the green ‘walk’ man, when a scooter tore straight through a red light and cut across in front of the pram.

‘What the hell?!’ I shouted and raised an angry hand.

To my surprise, instead of speeding off, the driver jammed on his brakes and skidded round to face me. He was a boy of about 15 or 16, black, slight, and snarling with fury.

He said: ‘You want to start? You really wanna start this?’ The baby and I were mid-road. The sun was bright on new tarmac, the pedestrian light flashing a countdown: 10, 9, 8…

Only the gang kids behave in this jumpy way, hyper-sensitive to disrespect. This was one of them for sure. In winter, like mice, the gangs go to ground. In springtime, in Islington, they come out to play, bringing with them a seasonal wave of knife crime and the ceaseless peacock-shriek of sirens.

Of course I didn’t want to ‘start’. Gang kids carry blades, sometimes big ones. Last year samurai swords were quite the thing, the year before, machetes. Keep quiet and carry on.

And yet… I’ve recently been helping the baby learn self-control. Don’t throw a fit, Cedd, just because your biscuit’s finished.

This furious boy seemed familiar. A toddler. Shouldn’t I stand up to him? Don’t we have a duty, as adults, not to let children boss us about? I flung my hand up again, indignant: ‘You went through a red light. You might have hurt the baby.’

This lack of respect was altogether too much for the boy. He revved the engine of his scooter and made as if to charge at us.

‘There!’ said the baby, excited. 3, 2, 1… I fled, and ended up, as it happened, alongside a police car with two of the usual fatty-puffs tucked inside. I knocked on the window: ‘That boy went through a red light!’

Obligingly, they hit the siren and sped off in pursuit and I sailed on, triumphant, to the park. There! It was only when the baby was squashed into its swing-seat, the adrenaline draining away, that I began to worry.

A gang from one of the surrounding estates arrived in our local park last summer. It became their base. They appeared each day as the light was lengthening, mostly black boys, some white, no girls and quite different from a non-gang group of kids. They smoked dope, dealt drugs, heckled passers-by and every now and then little flurries of violence would break out among them.

The park warden found knives in the bushes, and when he tried to confront them, he said, they threatened to kill him. At first they kept to a corner by the wall but, as the summer wore, on they became bolder and moved into the middle of the park, on to the benches by one of the gates. They sprawled across the path, making it clear who owned the joint. The under-fives football club, holding hands with their dads, walked in a wide circle to avoid them. Ladies with prams kept off the path and bumped along the grass. My husband, jogging along one lovely evening, saw one young gangster chase another across the park, and stab him in the leg. When police arrived, they arrested the victim because he’d stabbed another boy first.

One of the best books by the science--fantasy writer China Miéville is The City and the City, in which two separate communities co-exist in the same town without ever acknowledging each other’s existence. One set of citizens is taught to tune out the other, to ‘unsee’ them. Only in various agreed locations are they allowed to admit they’re aware of each other. When the gang moved in, the park became that agreed location for the unseeing tribes of N1.

Normally, we live in bubbles. Young hip-sters have eyes only for each other, dog walkers just for dogs. The melancholy bench drinkers stare into their cans. Come September 2016, the gang had corralled us into a functioning community. We whispered under the cherry trees, shared ideas, tried to decide what on earth to do.

The police would come if there was a stabbing, but who could we call on to just keep order — to reclaim our park? Who could pull rank with the hoodies?

The parkie was frightened of knives; the football dads were frightened of knives. ‘It’s just not worth it,’ everyone said sadly. It seemed surreal that in this affluent part of one of the world’s most civilised cities, there was nothing we could do to put the kids in their place. After a lifelong hatred of surveillance, I began to fantasise about CCTV. Maybe drones, I thought, circling constantly overhead uploading photos. In the end, only winter and the rain solved the problem.

The gang arrived back in the park a few weeks ago and they’re already bolder than this time last year. They drive scooters across the grass and shout at women. My sudden panic last Thursday as I swung the baby was that the boy would come to find me. If it made him that cross to be told off, he’d be spitting tacks that I set the police on him. Being in a playground was no guarantee of safety. There was a stabbing in a busy playground just round the corner in the summer of 2015. Last Saturday, in another part of Islington, someone threw acid in the face of a two-year-old in a pram.

In the end I called my husband, feeling pathetic, and requested an escort home. He arrived with a tennis racket to protect us. Rackets vs machetes. Just as we were leaving, laughing about my daft anxiety, a boy on a scooter tore into the park on the far side, followed by the usual gang on foot. Were they looking for someone? Just to be safe, I hid my face behind the head of the tennis racket and we slunk off.