Much credit for this is due to Westminster City Council. Rightly maligned for its recent council house corruption scandal, Westminster is one of the country's leading local councils in its policies on rubbish collection and street cleaning. An early enthusiast for contracting out such services to private business, the council now gets more bin for its buck than most others. As proof of the Westminster spirit, trials of hi-tech chewing- gum removal machines were held in Leicester Square on Monday.
Underlying these policies, however, is the discovery that the habits of a city's inhabitants are not immutable. Many Londoners who used to tolerate streets fouled by humans and dogs are now fed up. More important, a virtuous circle has been created. When people are already knee-deep in rubbish, they will drop a cigarette packet without even thinking; in an otherwise spotless street or park, they feel a pang of conscience.
In future, litter-conscious cities will face a dilemma. As the scope for improving the collection of rubbish and cleaning of streets diminishes, the focus of policy must inevitably move towards encouraging citizens not to create the work in the first place. Londoners can be nannied to an extent: Westminster, for instance, has 20 pairs of 'beadles' in sky-blue uniforms walking around market districts, politely challenging pedestrians and traders who drop litter, and using mobile phones to call the police if they refuse to accept 'litter tickets'. But Singapore-style solutions - fines for failing to flush a public lavatory, for instance - will be less well received.
A better target is air quality, where much remains to be done. Badly tuned buses and taxis are a leading source of London's grime and pollution - not because they exceed emissions limits (though some do), but because the limits themselves are far too lax. It is time for a new Clean Air Act.