What trousers to wear for the summer? If the advertising hoardings along a swish new development near the Mutton's residence are to be believed, Metropolitan Man 2008 leans nonchalantly on the balcony of his big-windowed converted warehouse in a pair of knee-length shorts, flip-flops/sandals and a T-shirt. But what if he needs to wear long trousers, like a grown-up? For a trip to a restaurant? Or his mum's? Or to work? And what if the jeans make him think of middle-aged petrolheads in leather jackets, à la Clarkson - a look about which I pass no comment, only to say not everyone can carry off Jezza's blokeish machismo.

Well, if he were Italian or French, he may opt for a pair of lightweight wool tailored trousers to go with an open-collared shirt. But though this European casual look is great on the streets of Paris or Milan, back home in the environs of back-garden drinks parties and trips to the pub, we often crave something a little more casual than what could be the suit trousers that we wear to work, sans jacket.

Enter the chino. The great thing about chinos is that they inhabit that greyest of areas: smart/casual. They are undoubtedly smart because they are a proper pair of trousers. It is important to define our chino as distinct from the cargo pant, an American style (like the chino) that has found favour over recent years and that often has chino-like fabric and colouring, but is distinguished by the presence of multiple pockets for carrying whatever it is that inhabitants of the concrete jungle like to have to hand.

The chino proper is another beast. For a start, it is clean, simple and flat-fronted. The lack of pleats is apparently down to a fabric-saving drive during the Second World War by the US military - and the provenance of the style is military through and through. Chino fabric is a type of twill, usually cotton, first used in British and French uniforms in the mid-19th century. Trousers in this fabric were taken up by Americans after US troops returned from the Spanish-American War in their military pants just over a century ago. The trousers were originally made in China; “Chino” is the Spanish for “Chinese”.

Today there is some confusion over the difference between chinos and khakis. The name “khaki” comes from the Persian word for dust, “khak”, and originally meant simply an earth-coloured hue used for camouflage by the military (first by the British in India during the Abyssinian campaign). Nowadays, the term applies to trousers that come more or less in earthy colours. For my money, khakis tend to be a little more casual and rough and ready than chinos, while chinos are a bit smarter and are often offered in non-dusty colours such as navy, grey and black. But in reality one man's chino may well be another man's khaki.

You'll find khakis at Gap (though sometimes, oddly, in colours such as “chino clay”). For chinos, my favourite destination is another US firm, Banana Republic. Here there's a great selection of chinos in different fits and varying degrees of smartness - from BBQ to boardroom. For the Steve McQueen in The Great Escape look - and let's face it, never has a pair of chinos looked better - go for a stone colour. The motorbike, however, is extra.