The intelligent consumer: Cashmerey separatists: the twin-set made in heaven

Investment buy or pure self-indulgence? The cropped, cashmere twin-set from TSE, pounds 338

Far away in the fearsome wastes of the Mongolian steppes, goats make it their business to grow the soft undercoat that insulates them against the bitter cold. Once every spring, the undercoat is combed out and shipped to Scotland, where it is washed in the soft waters of the Tweed and the Teviot and becomes cashmere. It takes 24 goats to make one coat and 40 different production processes to turn their fur into knitwear. They've tried to bring the goats to Scotland, but the milder weather means they don't grow their woolly vests.

In other words, there is a proper reason why cashmere is so mind-blowingly expensive. But the Mongolian goats don't entirely explain why a grey cashmere cardi by TSE (the "t" is silent) costs pounds 199 and one by Marks and Spencer weighs in at pounds 99. (To contextualise: a "designer" cashmere cardi by Clements and Ribeiro will set you back by pounds 320, so TSE aren't doing too badly). With the addition of a crew neck, the totals were pounds 338 and pounds 198 respectively.

It's a more than academic question since a little cropped twin-set, while a wardrobe staple, can be surprisingly hard to find. So, I broadened my scope a bit this week and also called in twin-sets by N Peal (total cost pounds 330) and Brora (pounds 248). All felt deliciously soft and luxurious: not surprising since all sourced their cashmere yarn from Chinese Mongolia (although not all were spun in Scotland). M&S assured me that they use only white cashmere (from a white beast) to ensure pureness of colour. They also pointed out that the vastness of their operation means they can keep prices low by buying in bulk. For their part, TSE argue that they produce a number of different styles in 25 new colours a season, on top of their eight basics - far more than M&S.

With quality so even, the choice came down to styling. I'll admit right away that we still don't have the perfect twin-set. Although neat on the shoulder, the TSE neckline is unforgivingly tight and both items are too long and too roomy to count as cropped. N Peal is certainly short enough, but fuller sleeves add unnecessary bulk. The Brora has a prettier neckline and a nice, snug fit, but a wider rib and generally more rustic quality make it unsuitable for evening wear. The M&S, finally, was never intended to be cropped. On the plus side, both M&S items have a flattering neckline.

As it happens I'm a massive fan of M&S, but even I can see that their colours for women's clothes are not good (why, when their knitwear for men comes in jewel hues?). They can do neutrals, but for anything more adventurous you'll want to go to the more expensive ranges.

So, with TSE you are paying for choice of colour, the exclusivity of a small company and a stylish label and I don't think that's worth the pounds 140 price difference. Ditto N Peal. Head to M&S if you don't mind the longer line. But for the closest approximation to that perfect twin-set at a very reasonable price, it has to be Brora.

For Brora stockists, call 0171 736 9944.