It was a dark and rainy night and I was cycling innocently home at about the speed of an elderly French onion seller, when – pok – something hit me on the side of the helmet. I heard a shout of laughter to my right, and a cry of "You ------!", and a car sped off up Shaftesbury Avenue. As anyone would in my position, I saw red. I put my foot down, and pedalled so hard that I was able to keep the weaving rump of the car in my sights, and I noted that it was some kind of Astra. Soon the bike had beaten the car. As they waited at the next set of lights, I pounded on the window. "Open up!" I cried. There were three kids inside, and I could see the culprit goggling up at me with appalled recognition. They lurched off again in the hope of escape, but of course I had them at the next lights. "Open up now," I yelled, "because you aren't going to get away with it, M*58 H*3! I am the mayor!" By this time they were starting to look a bit unnerved, and the window came down. "I know you is the mayor," said the driver, "and it was a accident." "Pull over!" I commanded. Eventually they pulled over in a street running up towards the British Museum. "Do you want me to get out?" said the culprit, who obviously had some experience of being flagged down by the law. "Er, yes," I said, noticing that it was pretty quiet around there. "Right!" I said, when we were all assembled. "Why did you throw something at my head?" "Please, Mr Boris sir, this wasn't meant to happen." "We know you is the mayor, man." "We gotta lot of respect for the things you are doing." "Hmm," I said, momentarily wondering where I was going with all this. "Whose car is this?" I demanded. "It's my uncle's. We are going back to Clapton after a day trip." "Right," I said. "And what is your name?" "My name is Derron." "And what is yours?" "My name is Erron." I didn't bother to ask the third chap, having by now more or less run out of ideas, except for a general desire to stop them doing it again. "Look, just don't throw things – er – at people's heads, OK." "It was a accident, I swear. It was only a piece of litter." At that point, I am afraid the red mist came down again. Only a piece of litter! Here we are in the depths of a recession, and councils in London are forced to spend about £100 million a year on cleaning up the casual detritus of people like him. Only a piece of litter, he says, when we all know that the number one environmental concern of the British public – far ahead of global warming – is the tidiness of their neighbourhoods and the plague of litter. It was only last week that the great Bill Bryson was again drawing attention to this desecration of our landscape, the 30 million tons we chuck out into public spaces without even the excuse that we are aiming at passing politicians on their bicycles. I don't know what the Astra passenger threw at my head, but whatever it was, it wasn't just a piece of litter. It was a national disgrace. We in London government are doing what we can. Bexley has a formidable recycling rate; Southwark has just announced a savage crackdown on anyone who spits out their chewing gum on the pavement, with on-the-spot fines of up to £80; Lewisham is asking its citizens to take photos of flytipping and post them on the web. Transport for London wants to ensure that no passenger leaving a Tube train has any difficulty finding a rubbish bin either at the station or in the immediate vicinity, and our work has been somewhat assisted by the recent extinction of some of the free newspapers. We are encouraging companies such as Addison Lee, which has supplied many excellent wall-mounted bins for butts and gum, and we are trying to devise a bin that will be elegant enough to be fixed to a listed building. We are still working on Wrigley and other chewing-gum makers to persuade them to put the harmless solvent in their gum that will save the councils a fortune in water-blasting the beastly stuff off the streets. We are planning action zones and clean-up-London days in the run-up to the Olympics. But in the end there is a limit to what the public sector can do to address the sluttishness of the public. We can mount blitzes, and issue exemplary punishments, but we can't tell every police constable or police community support officer to spend all their time issuing fixed penalty notices for litterbugs. We all need to feel a sense of shame about dropping litter. We will only feel ashamed if others have the guts to tick us off. It will not always be easy, as Isabel Dedring, the environment director at City Hall, found when she tried to reprove a man who was depositing a Coke can on a wall in Trafalgar Square. "What has it got to do with you?" he bristled. The answer is that it has everything to do with us. Litter is not only unpleasant to look at. It helps to breed a sense of insecurity and even crime. That is why I blew my top, and addressed the Astra trio as fiercely as I could: "Well, don't throw pieces of litter at people's heads!" I said. At which they did their best to calm me down. "We won't do it again," they promised. "Can we have a photo, Mr Boris?" I have no idea whether I changed their attitude to litter, but at least I tried. I hope you will, too. See The Daily Telegraph here for this column and more of the day's news and comments.