American book shops offer delights undreamt of on this side of the Atlantic. Walk past the self-help manuals, turn right at the horror and slip in by the thrillers and you’ll find yourself in the midst of heaven.

That’s Heaven and the Heather, of course. Because this novel, alongside Lord of the Isles, Highland Fling, Beyond the Highland Mist and Devil in a Kilt, is at the cutting edge of a popular revolution in romance writing that is taking the American publishing world by storm.

“Romance is an extremely lively genre at the moment,” explains Karen Kosztolnyik, the senior editor at Warner Books in New York. “It makes up nearly 40 % of sales in the mass paperback market.”

The facts speak for themselves. Romance sales brought in an astonishing $1.4 billion (£750m) in 2003. One in 50 American readers gets through more than 100 romances a year, and discerning fans have a bewildering array of settings to chose from. But though historical romances concocted among the ranks of the Pilgrim Fathers or set in the exotic South Pacific have their fans, this year the popular port of call for writers is Scotland.

It’s not hard to see why. “It’s the kilts,” explains Sue-Ellen Welfonder, the author of the bestselling Devil in a Kilt. “That or the men that fit in them. Scottish men are unbelievably sexy.”

It may be hard to believe, but 41.4m female readers cannot be wrong. Scottish women might think their men are about as attractive as a plate of cold porridge but in America, a man in a kilt is the most exciting thing since Mr Darcy hung his frilly shirt on a tree and went skinny dipping.

In Welfonder’s first novel, which bears a smouldering topless Scottish warrior on the cover, the devil of the title is Duncan McKenzie, an inarticulate blackguard whose heart is finally melted by flame-haired Linnet MacDonnell, a feisty lass with the gift of the second sight. After 420 pages of rough wooing, meaningful glances and struggling in the heather, Linnet and Duncan are finally . . . but no, I can’t spoil it.

“I love Scotland,” explains Welfonder, whose home on a Florida island is decorated with saltires, tartan throws and statues of Robert the Bruce. “I go there as often as I can and every time I bring back a stone. I have a special one from Lochindorb, a few from the top of Arthur’s Seat and another from Neist Point on Skye. They soothe me during the months when I am on deadline and can’t be in Scotland. There’s just something magical about the place.”

Millions of American romance readers agree, and they discuss their shared passion in a ring of members-only web discussion pages. When one recently invited members to discuss why romances set in Scotland were so popular, it was flooded with responses: “Rugged mountains. Towering crags. Lots of rock. Good for tripping over and being rescued from, or — even better — for leaning against during long, passionate kisses,” writes one online fan.

And there is no shortage of that in Welfonder’s book. Bosoms heave, lips are crushed and in one memorable scene, a caber is caressed. “Scottish men are so passionate and uncontrollable” says Keltictempress34, an online fan. “Just the thought of trying to tame one makes me feel weak at the knees.” “And the warriors!” agrees Wantonlass. “The thought that one could seize you and take you back to his Highland castle in the Borders (sic). ”

At her publishers, Kosztolnyik taps into this mood. “I think part of the appeal for readers is that the Scottish hero is a sexy one, and it takes a special kind of woman to tame him. But he has a loyal side too, which you can see in the Scottish clans. That kind of extreme loyalty is very appealing to women readers.”

And what about that little-known Scottish trait, “raunchiness”? “Modern romances really are on a spectrum between the very old-fashioned and chaste and the very erotic,” explains Karen. “Some are very spicy.”

They certainly are. Randomly flicking through some of the bestselling Scottish romances, I found a full-on frolic in a loch, six tumbles in the heather, a couple of cairn- top cavortings and a tryst in the Trossachs.

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