Joan Smith: Excuse me, you've dropped your green credibility

I used to have a beautiful pair of dark green suede stilettos, until I stepped in a horrible, sticky wad of chewing gum on my way home from a party. Not long after that, a friend arrived for dinner on a dark night and trailed dog faeces through the house, not realising she'd picked it up on her shoes. It's not unusual to find drink cans and crisp packets in my front garden, as though some ambulant snacker has passed in the night and couldn't be bothered to take their rubbish home.

What is wrong with these people? I've never dropped litter in my life, and on the rare occasion I inadvertently let go of a chocolate wrapper or a till receipt, I pursue it down the street with a burning sense of guilt. For years I picked up litter and handed it back to people who'd just dropped it, politely suggesting they dispose of it in a bin, but now I stop myself accosting litter louts because of the danger of being verbally abused. Even so, the scruffy state of British streets drives me mad, and the problem is getting worse, according to Whitehall and the campaigning organisation Keep Britain Tidy.

Levels of cast off sweet wrappers, non-alcoholic drink containers and fast-food cartons have all increased over the past 12 months. Smokers are the worst offenders, with eight out of 10 sites in an official survey blighted by cigarette butts; we've seen those forlorn huddles of smokers outside offices and shops, furtively lifting hand to mouth; an amazing number leave their detritus behind on the pavement when they return indoors. There's been a 4 per cent increase in hazards from chewing gum, and a rise in dog fouling in the winter months. Graffiti in shopping areas is at its worst level since this annual survey was first carried out.

What's weird about this is that it's happening at a moment when people claim to care more than ever about the environment. I'm delighted that so many individuals say they're worried about the ozone layer and greenhouse gases, busily calculating their carbon footprint. But what about nearer home? A substantial proportion of the population does not drop litter, but a campaign has just been launched to address those who do; it's called Love Where You Live, making the point that we share public space – high streets, shopping centres, parks, cinemas – and it's better for all of us if we look after it.

Dropping litter and gum is a form of bad manners that holds up two fingers to thinking about the effect of our actions on others. Occasionally, it's something worse, indicating an aggressive attitude that may spill over into terrifying violence on the slightest pretext: three years ago, 23-year-old Evren Anil was killed confronting two teenagers who had thrown a sweet wrapper into his sister's car at traffic lights in south London.

At a time when public money is in short supply, littering is expensive. Clearing up bus tickets, takeaway food cartons, plastic bags and cigarette butts cost an astonishing £858m last year in England alone, an extraordinary waste of money that could be spent on maintaining essential public services. And this underlines the need to change public behaviour. Offenders should be pursued and fined. Business could help by introducing refundable charges on cans and bottles. But it also takes education to make individuals feel part of civil society. Younger people, especially, support environmental causes, and a simple message needs to be got across: there's nothing green about being a litter lout.

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