This, unfortunately, was exactly the question I was about to ask. "Why? Well, we don't rip anyone off and these are pashmina," she says patiently. "You can't compare them to woollen scarfs. That's like comparing purest silk to a pair of cotton underpants at Marks & Spencer."
The style guru Lucia van der Post has decreed that the pashmina is "the most chic shawl around town," and if you have to ask, then be careful how you do. It seems that something called the shatoosh used to be. It was to die for - ask the antelope that supplied the fine and rare fibres for the cloth and has since become endangered. Well, at least someone had the sense to quit selling them before Sting made a record.
But there is still pashmina or even the odd vicuna to shrug into. Pashmina is made from the hair combed from the underbelly of the capra hircus (it means "hairy little goat") that lives in highest Kashmir. "This skill is unique to the Kashmiris and they will not show you how they do the weaving," says Ms Trehearne, who sells direct from her Hampstead house and whose other career is as an English literature academic.
To find the vicuna, you have to go half-way around the world to the Puna - the cold South American steppe. Down to only a few hundred in the mid- Sixties, the small animal related to the alpaca and llama has made a healthy enough comeback to be back from the brink and back on the shelf at Harrods. A small shawl is pounds 849, a large one pounds 1,949.
Why? Well this is no ordinary wild ruminant. The Incas sacrificed them on a fairly regular basis, but then they had some one million to cull from. We can blame Pizarro, who plundered herds for New World silk and began a trend that didn't end until the Sixties trade ban.
Now there are 160,000 vicuna but, if you count them in ounces of fleece, that is still not many. Each produces only eight ounces every two years (compared to six to eight pounds per year by the merino sheep). An overcoat requires a veritable herd (25 to 30 of them).
It is hard to tell which is more politically correct. The fleece from an animal given special permission to be shorn by the endangered species watchdog CITES, or goats scampering across the political divides of strife- torn Kashmir? Who needs fur when you can play New Age one-upmanship at this sort of level?
Back at Ms Trehearne's house, my knees are now molly-swaddled in pashmina. "Isn't it warm? It's like a thermal vest. You can hatch an egg in one, though my greengrocer said that is a very expensive way to hatch an egg."
She unfurls one covered in the tiny stitches of a master embroiderer. "Of course, something like this is very expensive - we want pounds 4,000 for it - but then again it took one man three years to do." Suddenly, Marks & Spencer seems very far away indeed.Reuse content