Last week a friend showed me a bale of peacock blue Harris Tweed she'd bought from a weaver in South Uist, which she's using to make me a cushion.

This will be beautiful, but as I touched the fabric and saw its colours deepen with the light, I wished my ambitions had been a little grander, that I'd asked for a swirling cape, say, or a dramatic wall hanging, so that the moody material would be given centre stage.

Tweed has that effect, it seems. The recent announcement that a major Chinese textile firm, Shandong Ruyi, is to buy a share in The Carloway Mill, on Lewis, is just the latest bit of good news for this industry. It's hard to imagine that only a few years ago, as sales dwindled and fashion appeared to have bypassed this noble cloth, Hebridean weavers were wondering if they should pack up their looms. Now it is one of the most desirable fabrics on the catwalk. Glitzy fashion houses, such as Alexander McQueen and Chanel, have adopted it as a heritage material that captures the craze for vintage, but also radiates quality, durability and – above all – luxury. That even the likes of Marks & Spencer and John Lewis are using it in their collections shows how far, and how fast, Harris Tweed's fortunes have changed.

In the wake of this contract, the manager of The Carloway Mill admitted she's having trouble finding enough new weavers to meet galloping demand, given how few places are available on the three-month training courses they require. That apart, the Chinese partnership means weavers will be able to earn a full-time living, rather than view it as seasonal work, which was the way islanders originally managed to combine their craft with their croft.

As Hebrideans raise a toast to their good fortune, however, spare a thought for their cousins in the south. While there was also a welcome boost last week for Dumfries and Galloway textile firm Reid and Taylor, who secured a prestigious Chinese order, in the Borders town of Innerleithen their mill is hanging on by a thread. The oldest operating textile mill in Scotland, Caerlee Mill nearly faced closure three years ago. At that time 132 jobs were lost. Now under receivership, its remaining 36 staff face the threat of redundancy.

The differences in fortunes across the country could hardly be more stark. If cashmere were going out of fashion it would be easier to understand, but as a reporter from New York Fashion Week in February gushed: "Cashmere suddenly seems to be having a full-on menswear moment" – so much so that even a deer-leather motorcycle jacket paraded down the runway came with a cashmere lining. Far from dipping, demand for luxury knitwear seems to be soaring.

Is there anything the tweed industry can do to help its southern kin? Other than offer them a retraining in tweed weaving and opening a satellite operation, it seems unlikely. Part of the triumph of tweed can be explained by simple economics. One of the original cottage industries, today, as 300 years ago, tweed weavers are self-employed, buy their own equipment and work from home. As in many other businesses, the cost benefits of this easily undercut the overheads incurred by factories, mills or offices.

There is another crucial difference between knitwear and Harris Tweed. Only tweed is synonymous with Scotland. Like Stilton or Camembert it cannot be made anywhere but on its home turf. Not only do the weavers' ancient skills bring a cachet to their product, but the well-known history of the material and its making evokes romantic images of old Scottish life that add an allure no other fabric can match.

My partner once had a heathery Harris Tweed jacket that could in theory have seen him from first pay cheque to state pension, had he not decided, after quarter of a century's dogged wear and the odd elbow patch, to bury it and thereby nourish the lawn. Now, he has a new tweed suit on order. This will no doubt become an heirloom, because as all who've ever worn it know, this material is almost indestructible. If only the same were true of mill workers's jobs on the banks of Tweed.