When the literary map of Scotland comes to be drawn, and the cartographer sticks the little flags on Abbotsford, and the auld clay biggin, I hope there will be one for Granada Services on the M9 near Stirling.

For David Gray-Buchanan of Edinburgh and Susan McClymont of Crieff, it was once the halfway house where, for the price of a coffee and a sticky bun, they sat across a table and wrote the most original Scottish children’s theatre since JM Barrie.

They are a couple of originals themselves. They first met through their children, who went to the same playgroup. He was a musician and she sang, so they made up children’s songs. They tried their hand at folksong, and started entering folk festival and Radio 1 competitions. They got into finals, but gave up in face of the hauteur of the other folkies who found out the pair had never sung in a club or a pub before.

If all that seems mildly ridiculous, then their next career move, “to try and make some money writing for theatre”, appears hardly more sensible. Neither of them had any background in theatre, no local dramatic society, nothing. “That helped us. We didn’t know what we couldn’t do. We didn’t have any boundaries. We still don’t.”

Their fantastic imagination demands superb technical work, andor a wad of money. As Robert Rae of Edinburgh’s Theatre Workshop observes, “With these two, you have to suspend your disbelief in funding.”

The pair of innocents needed sympathetic directors. The first was Donald Smith of the Netherbow, who was “very encouraging, very sympathetic, even though the scene we sent him was really badly written.” They spent the whole of the following year working that scene into Phoenix, a wholly magical play set in a workaday farm in Perthshire, when the world’s seasons have stopped and the ritual tokens to re-animate them are brought back by seafaring Uncle George. In sequences of brilliant and unnerving theatre, the farm children are assailed in turn by the demons of Water and Fire, Wind and Water, as they come to reclaim the icons.

The play was premiered in Ken Alexander’s production at Perth in 1993, and repeated the following year, when reportedly the previous year’s audiences were still talking about it.

Two years later, the same team produced The Silver and the Red, again discovering the supernatural in the everyday.

I remember the stgecraft and storytelling startling the audience in ways that had the school parties looking to their teachers for reassurance.

At Granada, they used to meet at 11am and work until school was out, or after the children’s bedtime until 11pm.

Nowadays the workload has increased, so they have an office in Crieff (cheaper than Edinburgh), “where we do all the thinking and the shouting.” They continue to write separately in their homes, and then meet to compare scripts.

They are neatly matched as co-writers: he is strong on the bizarre imagination, the creator of the fantastic storylines; she, once a journalist, brings the discipline of accuracy and precision to the dialogue. They rewrite constantly, especially in the first weeks of rehearsal. “The play gets shorter every time,” they wail, as they adjust to give more room to the actors.

It astonishes me that they are not well known names in the theatre community. They put it down to being uneasy with self-publicity (which they seriously are), staged in Perth rather than Glasgow or Edinburgh, and “not fitting in an Arts Council box”.

For example, Phoenix could only get funding as theatre in education, which strictly speaking it is not.

It’s a marvellous play for children, with no connection with Christmas, and therefore in a cultural limbo. And of course they suffer from working for children.

“At a writers’ conference, say you’re a writer and they’re agog.

“Add that you write for children and their eyes glaze over. That really annoys us,” says Susan McClymont.

The future looks brighter. On Monday at Gilmorehill in Glasgow, Birds of Paradise (a company created specifically to deal with disability issues) launches Merman, a new play, for a six-week tour.

The company commissioned it, and Tina McGeever, one of its directors, offered them a simple image of children seeing someone in the sea. From this they have conjured “a scary story” out of the way children’s imagination plays on the adult world.

Looking further ahead, Ken Alexander is planning to direct their new blockbuster at the Byre next year. Still with its working title of The Glashfell Cave, it draws much of its energy from Shamanism and cave painting.

It will complete a trilogy that should be end-of-year treats for primary schools for years to come. Given that niche in the repertoire, the writers would have their recognition, and their families some reward for their bewildered and resigned support.