A GROUP of twenty-something office workers passed me one lunchtime, laughing about somebody they called a Muggle. In their Paul Smith suits and nude high heels, they looked far too sophisticated to be talking out of a children’s book. Yet I realised that, for their generation, Harry Potter and his pals were a shared bond.

Not to know who Draco Malfoy or Hagrid were, or the finer points of Quidditch, was to have been living in outer darkness, wearing earplugs, during their formative years.

Is it really only 20 years (and a day) since Harry Potter and the Philosopher’s Stone was published? It feels as if HP – whose phenomenal success means he has probably outsold the sauce – has been with us for much longer.

Barely a week passes without some mention of the books, films or plays, or their fabulously wealthy author. Regardless of their critical reception, the attention J K Rowling attracts is light years away from the publicity accorded to the likes of Robert Louis Stevenson when Treasure Island came out, or Edith Nesbit when she wrote The Railway Children. The profile of children’s writers has come a long way since then.

Clearing out papers at the weekend, ahead of moving house, I came on notes I’d made when interviewing Rowling for her third novel, Harry Potter and the Prisoner of Azkaban. That was in 1999, and one of the last occasions when arranging to speak to her was easy. By the time book number four was published, a portcullis had been lowered and sentries set at the gate. We sat chatting in an Edinburgh cafe, and she spoke unguardedly, a sparky, nervy, self-effacing woman who nevertheless had not one iota of uncertainty about the books she was writing, or why.

People, she said, asked if her instinct for what children liked to read came from her teaching days, or from having a child. “I get it all from remembering what it was like to be a kid,” she said. “So everything Harry goes through, and all these feelings of being lost sometimes and confused, these are all things I remember really vividly.”

PhDs have doubtless been written on the significance of the series, and the moral complexities and literary influences it contains. For ordinary readers, however, it is very simple. Hers are great stories, well told, by an author who, far from condescending to her audience, is at pains to show that she is on exactly the same wave-length.

Harry Potter could not have arrived at a better time. In cash-strapped, post-Thatcher Scotland, the arts were seen as a luxury, something councils and schools and governments could barely afford to support. Despite the country’s much-vaunted educational system, literacy was not a strong point – a fact that, sadly, shockingly, remains true today. The volt that Rowling’s books sent sizzling through the cause of reading has yet fully to be quantified, but no-one can deny it was electrifying.

And as a result of her success, the children’s book industry suddenly began to fly, catapulted from a worthy corner of the publishing trade to the shop window. In so doing it initiated a literary and cultural revolution that continues to this day.

It is astonishing, and moving, to think that an unpublished writer’s obsession – to use Rowling’s own word – with her hero and his mates could bring fresh colour and excitement into the lives of millions. There was nothing remotely similar when I was a child, no feverish anticipation about a forthcoming book that would see us queue at midnight for copies, or read through the night so we could discuss it with our friends the next day. Whatever reservations those from the analogue age might have about hype and the wiles of marketing executives, these books have found their way into more young – and eager – hands than any other novels.

The influence they have had is incalculable. Indeed, the first Harry Potter title is the fifth best-selling, single-volume book ever recorded.

It is a mind-boggling fact, too big to comprehend. But what is easy to understand – because the results are visible – is the effect good books have on children. There has been no lack of world-class children’s writers in this country, of course, and Rowling follows in the wake of George MacDonald, with his eery tales set in the Highland silver mines below ground, RLS – who created not just Jim Hawkins and Long John Silver but David Balfour in Kidnapped and Catriona – Kenneth Grahame, with The Wind in the Willows, and J M Barrie’s Peter Pan. Then there are our modern writers, among them Joan Lingard, Theresa Breslin and Julia Donaldson, Alexander McCall Smith and Julie Bertagna, and far too many others to list.

Writing for children in this country no doubt has flourished partly because of our fairy story heritage, and partly thanks to a school system that puts such emphasis on reading and writing. Compared with many countries, this has always been a place where to be a children’s writer is a source of pride.

The imprint of this on the imaginations and ambitions of centuries of youngsters is difficult to assess but, without a doubt, it left its mark. The best children’s books give readers hope and inspiration, and fire them up to enter the world on their own terms. Is this what inspired our great inventors, travellers, and scientists?

Quite what makes a classic is impossible to define, yet there is no mistaking the power of good stories. The other day, a 10-year-old was browsing our bookshelves. A fan of The Hobbit, and half way through The Lord of the Rings, he was keen to read The Silmarillion next.

His eight-year-old brother, asked what he liked to read, simply answered, “novels”. He left, already immersed in Just William, which he finished later that day.

It is too early to tell if Harry Potter will one day join the ranks of the immortal greats. What is sure, though, is that, unlike almost any other children’s writer that came before, Rowling made reading cool. That we remain bedevilled by literacy problems makes you wonder how much worse things might have been without her.