The woman in the playing field looks respectable enough. “Expensive-looking hair”, I think; “pricey jacket”. Her dog is big and rangy. He gambols around her feet, before bounding several feet away and squatting, writes Matt Gaw.

The woman chooses that exact moment to turn away, taking out her phone and making – or at least pretending to make – a call.

Seconds later her dog is up and running across the field, kicking up grass and looking generally pleased with himself. The woman, perhaps sensing that her dog is done, has already put her phone away and is moving to follow her pet.

“She’s not going to pick it up, she’s not going to pick it up”, I say to myself, pushing the youngest in the swing. Secretly, I will her to walk away to justify my growing sense of moral outrage. I let her walk for ten paces before speaking. I want her to feel like she’s gotten away with it.

“Excuse me, I’m not sure if you’ve seen, but your dog just did a poo”, I say it in the most neutral tone I can manage. The woman looks at me straight in the eye. “Brilliant”, I think triumphantly, “she knows I’m accusing her and there’s nothing she can do about it.” With a moody flourish she pulls a bag from a well-tailored pocket and tidies up.

I feel like Columbo. Bumbling, yet sharp; scourge of the anti-social faecal deposit.

Walking home with the kids I think about a passage I’ve read from Bill Bryson’s new book The Road to Little Dribbling: More Notes from a Small Island. In one of the scenes he describes how a well-heeled pensioner spends £20 in a Lake District café, but leaves a paltry 10p tip – dropping it into an empty bowl by the till.

“I am guessing”, he writes, “she assumed that it was full of coins already and that hers would disappear among many others, but when I stepped up I could see that the bowl had a solitary 10p coin in it.

“Am I wrong or is this becoming a feature of British life – behaving in quietly disgraceful ways when you think no-one is watching? I am not saying that this is exclusive to the British or that it is universal among them by any means. It barely used to exist at all and now you see it pretty regularly.”

I admit, at first I thought Bryson was being nostalgic. But now I’m not so sure, I think he’s on to something.

The passage isn’t about young people who are behaving badly (the stereotypical youth of today) it’s about us grown-ups. Outwardly respectable people who do bad things when they think they can get away with it.

It’s that childless 4x4 driver who takes up the family parking space in Waitrose or that father who forces his offspring to hold a table in a busy restaurant while he queues to order – leaving people with groaning trays looking for a seat.

I feel a pang of guilt too.

I might not bedeck fields with dog muck, but I’m sure I’ve committed more than my fair share of selfish misdemeanours; the secret BBQ on the BBQ-free beach, claiming that one of the kids lost my parking validation, feigning urgency to accelerate an airport check-in.

I hang my head.

Later I’m talking about the misbehaving middle classes to my wife. She laughs and shows me a series of pictures she’s taken on our street.

They are images of dog poos. In each photo the offending deposit has been carefully drawn round and someone has chalked a slogan above it – “Poo shame”. “It seems like some people are fighting back,” she says.

They are not the only ones. Leafing through the paper there is a picture of a group of dog walkers in Bury St Edmunds who are calling for public humiliation and fines for those caught fouling.

In Leiston one man was said to be so incensed by dog mess he hid in the bushes to catch owners in the act.

The image of a furious man crouched in the undergrowth desperate to catch his own expensively-jacketed dog walker makes me laugh.

I’m still chuckling when the cat starts scratching at the back door.

Opening the latch, I bend down and tickle him under his chin. “Come on then, out you go”, I say, before adding in a low whisper, “But don’t poo in our garden.”