I recommend to you, the grey flannel trouser. For wear as an alternative to jeans, for wear with almost any kind of jacket you can think of, and for wear as a delightful foil to all types and shades of leather footwear.

The grey flannel trouser has not become the ubiquitous mate for an odd jacket for nothing. As a colour, it lacks its, reducing the chance of clashing with navy/green/brown or whatever shade is worn on top. As a texture, it has enough nap to provide some great surface interest yet remains clean in finish, retaining its smartness.

It is not a pair of chinos, which will always have associations with workwear and are inherently casual as a result. Neither is it a pair of worsted wool trousers, which are always too smart too wear with boots or more casual shoes, no matter how they are woven. The grey flannel is the perfect partner.

I have a strong memory from when I was a teenager. Five of us were sitting around in a circle in the back of a taxi (for American readers, a Black Cab in the UK has three seats in the back facing two folding-down seats opposite). Sitting in such close proximity, our knees were close together as if comparing the various pairs of trousers we were wearing. Except that there wasn’t much variety: we were all wearing jeans, all in a mid-blue, with perhaps slight tweaks in design and cut.

I’m not suggesting we should have been wearing flannel, particularly as teenagers. Well-cut chinos in different shades would have been the best choice, followed by a moleskin or similar cotton. But I’d put money on the fact that those friends still wear denim every day they don’t have to wear a suit. And nothing else. Unless it’s hot enough for shorts.

Now that they are in their thirties, they should have really moved through chinos, mastered moleskin and started to experiment with more grown-up cloths like flannel.

Like any item of clothing, the effect of a pair of grey flannel trousers is still very much determined by its neighbours. With a pair of tasselled loafers and a blue, gilt-buttoned blazer, they can look frightfully staid to some people’s eyes (although, as another caveat, much of that effect depends on the cut). And even with suede lace-up boots and a Harrington jacket (a combination I sometimes wear on the weekend), they can seem very dowdy.

Get the cut right. Sitting on the hips, rather than the natural waist or below the hips as most young men today wear jeans. Fitted but not tight through the seat and thighs, tapering slightly below the knee to finish with an opening somewhere between 7 ½ and 8 ½ inches. In a mid-grey, the greatest danger being that they are so dark they look like they could only belong with a suit; the only danger of being too light is that they look out of place on a dark, wet day. I wear mine without belt loops, preferring side buckles as I would have on a suit; but the ability to add a belt will make combinations easier to pull off and tweak according to the formality of the occasion. And get them in a slightly heavier cloth than you would instinctively – remember, cloth wears far cooler on the lower than the upper half, and a heavier cloth drapes better.

That’s it. Go experiment with flannel, and look up some of the preppy style websites (or indeed any Ralph Lauren campaign) for tips on what to wear with them.