Last Saturday night I became an example of what is wrong with Britain today and I bitterly regret it.

It happened like this: a warm night, strolling to our cars after a theatre evening with friends in a quiet market town, we saw a bunch of kids standing around a parking meter. Some balanced languidly on skate boards, others just slouched. All were watching one boy.

Aged about nine or 10, dark-haired, wearing jeans and a Man-U T-shirt, he was robbing a parking meter. Not money, but tickets. A cascade of them hung from the machine, and as we approached he pressed something and another one appeared.

'What are you doing?' I asked. 'Nothing,' he replied. I could see he had one of those small wooden spatulas you get from the chip shop, and as he pressed this against something on the machine another ticket whirred out.

Mistake number one: I didn't say, 'Where did you get that?' Because I knew. We had been in the chip shop a few minutes earlier when an even younger, blond-haired boy came in to get some. The fish fryer asked what they were for and no one believed him when he said: 'My mate's got some chips at home.' But nobody stopped him running off with a handful.

'What d'you want them for?' I asked the ticket boy. 'For the 50ps,' he replied, and proudly showed me the detachable sticker on the back of each ticket offering 50p off entry to a local leisure centre.

Mistake number two: For a moment I admired the enterprise. He had spotted a gain, found a way of obtaining it and was working for his own benefit.

'Don't you know this is stealing?' I said. 'What?' He looked genuinely surprised. 'Stealing]' I repeated. 'These aren't yours. You shouldn't be having them.' 'Yeah,' he said and pressed again.

Mistake number three: I should have taken tickets, wooden prodder and boy to his home and asked his parents why they let him roam the streets at 10.30 on a Saturday night.

Instead, I shrugged and walked to the car. 'Children today,' exclaimed one of my friends.

But today's children are the result of today's adults. Unless we tell them what's right and wrong, how will they know? And that's not just a job for parents, teachers or the police. We all have responsibility. And here's the real cause of my distress: I'm a teacher. When people complain that schools don't show children sufficient moral lead, I will argue that our task is made almost impossible by the tide of amorality that has flooded all areas of British life.

But, as a citizen on Saturday night, I joined that tide. Faced with wrongdoing, I showed no serious disapproval - words don't count with kids, it's what you do that they take notice of.

Unlike some adults who have tackled young lawbreakers, I wasn't in danger and I know how to deal with small boys - it's my job. Have I simply become part of the 'walk on the other side' zeitgeist that has encouraged the elderly to turn their homes into fortresses and women to avoid travelling alone? If so, I'm scared. If mature citizens like me can be so desensitised, what hope is there for young people?

As for the boy, he will be encouraged in his thieving career by knowing that other adults will probably walk away as I did. Or so I thought, until a police van with light flashing raced into the car park and the kids scattered. A good citizen somewhere had felt sufficiently affronted to do something about - and for - the dark-haired lad.

It didn't make me feel any better.