At 53 she’s young to be a grande dame. But two significant events in consecutive months confirm that, in a characteristically unfussy fashion, Judith Weir has slipped to the fore-front of British musical life. Just before Christmas she became the first composer to receive the Queen’s Medal for Music – beating better-known figures such as Harrison Birtwistle, Thomas Adès and James MacMillan to the honour. The accolade was all the sweeter because the committee advising the Queen included two fellow composers: Sir Peter Maxwell Davies and Michael Berkeley.

Now this hugely admired figure – who has inspiringly pioneered community and educational projects as well as writing some of the most enjoyable vocal and orchestral music of our time – is the subject of one of the BBC’s all-embracing composer festivals, live at the Barbican and on Radio 3. Starting today, it embraces a dozen concerts, plus films, educational events, foyer entertainments and talks – and has clearly left Weir dizzy with delight. “Even the fringe events done by the Guildhall School represent more music than I have ever had played in London up to now,” she says.

The festival is called Telling the Tale, and that’s a perfect three-word insight into Weir’s special talent. Even in her orchestral works, a tale is being told – the more fantastical and ironic the better. “Perhaps that indicates a road not taken in my life,” she says. “Maybe music by itself doesn’t quite satisfy me.”

That’s apparent not only in the opera being performed tomorrow night – The Vanishing Bridegroom, which ingeniously meshes three old Scottish legends – but also in the brilliant music-drama that first brought her fame, in 1987. That was A Night at the Chinese Opera, a masterly fusion of whimsy and tenderness, comedy and tragedy, clothed in the conventions of Chinese opera and fashioned with the lightest of touches. “The exact years when I was growing up – 1966 to 1976 – are now referred to in China as the Ten Disastrous Years, the period of the Cultural Revolution,” she says. “China was constantly in the news, and of course it was all about young people. I got interested. Then I got interested in the hundreds of little Chinese dramas written in Kublai Khan’s time. So when I was suddenly given a chance to write a piece for Kent Opera, I decided to turn this material into an opera.”

A very different tale is told in the big new choral and orchestral piece that will end the festival on Sunday. Called CONCRETE, it is, in Weir’s words, “an imaginary excavation” of the Barbican Centre itself, “burrowing through 2,500 years of historical rubble”. What got Weir interested in that?

“I began to wonder how a development of this size comes to be built on prime London land. So I started reading about the area. I’ve always wanted to write about London history, and also to get beyond the clichés always used to represent the civilian experience in the Second World War: you know, Vera Lynn, and people huddling in Tube stations.”

Yet if it wasn’t for the Blitz, the Barbican would never have been built. “Exactly. It was just one raid that did it. They were using incendiary bombs, and so much of the old City was wooden. But interestingly, as a result of that raid several sections of the old Roman wall were revealed, as well as the Temple of Mithras – a religious cult, originating in Egypt, to which many Roman soldiers belonged. I wanted my piece to show that London has always been a place through which people moved, but left their mark.”

Despite her Scottish heritage, and the years teaching in Scotland, Weir grew up in the London suburb of Wembley, and now lives in London again. She starting composing when she was at North London Collegiate School, and took a music degree at Cambridge – but never thought of becoming a full-time composer until well into her twenties. “I was still confused about my direction,” she says. “It was a difficult era for music anyway. The world was coming out of modernism, and it wasn’t clear what was good or bad any more.”

Even as a student, she bravely resisted the prevailing pressure to write complex serial music – preferring to develop her own quirky brand of tonality. “I didn’t disrespect that Boulez territory, though I do think you are a prisoner of your own peer group if you write in that style. Almost the only people who respond to your music are your own rivals! But I just couldn’t have written that stuff myself.”

Even in the 1970s she was listening to American minimalists such as Steve Reich and Terry Riley. That suggested one new direction. In Glasgow she found another. “I happened to share a house with a folk musician. So, without meaning to, I got into the world of bagpipes. That opened other windows. I saw that there were many ways of structuring extended pieces of music.”

For a living composer to be show-cased over a whole weekend is, she acknowledges, a rare marvel. “As a composer you feel very much on the edge – even of the classical-music world,” she says. “But I don’t mind that. I think it appeals to my temperament.”

Does she have another opera in the pipeline? “Yes,” she replies. “I think it’s now or never. I find composing exhausting, and an opera requires more energy than anything. But I can’t tell you anything about it, because I don’t yet have a subject.”

— Telling the Tale runs from today until Sunday at the Barbican (0845 1207549, www.barbican.org.uk ). Scottish Opera’s Night at the Chinese Opera opens at the Theatre Royal Glasgow on April 11 (0870 0606647)

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