The wonderful wizard of Oz

This week the Royal Philharmonic Society paid tribute to Sir Charles Mackerras, Australian (by birth) and honorary Czech (by way of Janacek)

It's appropriate that this week's recipient of the Royal Philharmonic Society's conducting award was unable to accept it in person: Sir Charles Mackerras was busy at the Royal Opera House, conducting a work he'd helped rescue from oblivion. For it was his idea that the aborted first version of Martinu's The Greek Passion should be reconstituted from pages scattered round the globe; to his gold star for conducting should be added a further one for musicological tenacity.

As a boy in Sydney, he had begun on the piano but gravitated via the flute to the oboe because, for obscure reasons, Second World War conscription had left oboists in short supply. Migrating to London, he became an oboist at Sadler's Wells, also began to conduct, and to discover what makes singers tick.

One day in 1947, fate took a hand. "I was sitting in a café reading a miniature Dvorak score," he recalls, "and a stranger opposite leant over and said 'I see you are studying the music of my compatriot.' I told him of my ambition to be a conductor, and it turned out that he was a refugee cellist who had just come from the Anglo-Czechoslovak Friendship League armed with information about exchange scholarships. He suggested that I apply."

Mackerras got one, went to Prague, saw Janacek's Katya Kabanova and was bowled over by it - and the rest is history, both his and ours. "Nobody ever needed me to point out that Mozart and Handel are great composers," he says. "But after the war, we did need someone to speak up for Janacek."

He did, and with a vengeance. He began cleaning up the scores - successive generations of conductors had sweetened their astringent textures - and he also made discoveries, one of which didn't please Prague's music fraternity. "It was as if a Czech musicologist had come to London and found another Enigma Variation." Eventually accepted as an honorary Czech, he was invited to reopen Prague's Estates Theatre with a production ofDon Giovanni - which had premiered there.

The middle of the 20th century was a turbulent time in Czech politics, with hopeful thaws alternating with savage crackdowns, and musicians often feeling the lash. It was Mackerras's good fortune that his mentor Vaclav Talich was put under house-arrest, and was therefore able to tutor him intensively.

During his time in Prague, and an even longer one in East Germany - where he conducted better-quality orchestras than he would have been offered in Britain - Mackerras spent his unexportable fees on building a huge library of scores, and turned himself into a musicologist. "In those days, such people weren't taken seriously by practising musicians - they were regarded as cranks." His radical achievement has been to get the two groups talking, and to inject musicological insights into musical practice.

In Mackerras's view, Wagner was the first composer to write down exactly what he wanted: before him, it was all a matter of shorthand hints, which mean that today's interpreters have an inescapable responsibility. "When you come to a completely unpianistic passage in one of Mozart's concertos - a piece he'd have played himself, and for which, in places, he only wrote an aide-mémoire - improvisation and embellishment is essential. And the same holds true for voices. When Mozart could trust a singer to ornament on her own, he didn't bother to write it out."

Mackerras's own ornamented version of Le nozze di Figaro - based on his reading of manuals and treatises - divided the critics, as did his reornamented Handel. And Handel was a harder nut to crack in that, with him, even less can be discovered from period sources. "For that," Mackerras says jauntily, "I relied on my instincts."

His experiments with pitch have been controversial too. "I have always pitched things to suit the singer, as Handel did. But the big difference between the 18th century and today is that - apart from the fact that singers now make a much louder sound - is that they sing much higher in the chest voice. Composers then set their climaxes not on a high note, but a low note. Today's singers want to end high - and you have to persuade them not to."

Get him on the subject of singers and he's hard to stop. It's strange but true, he says, that women find it harder to sing comprehensibly in a high register than men do: while high tenors sing words, sopranos sing sounds. And with regard to the diction debate, he never knew the Sadler's Wells brigade - precursors of English National Opera - to have any trouble with words. "But now, if you ask singers to enunciate clearly they make a face and say "It would spoil my line". It didn't in the old days - they could sing words and sing beautifully. Some still can - with Anne Murray or Philip Langridge or Bryn Terfel, you never miss a thing, any more than you do with Pavarotti, for all his faults."

It's perhaps better not to get him going on the subject of directors. His famous walk-out from Richard Jones's production of Giulio Cesare - which included a dinosaur and a man with a fridge on his back - is a matter of mingled pride and regret. "He never explained what the images meant, or felt any obligation to. A man ought to be able to make clear what he believes, and why." Deborah Warner's Don Giovanni - in which Dona Elvira, seeking revenge, came on with a street-map - earns his jovial derision. "Subtexts are all very well, but not if they take the piss out of the opera."

It's no surprise that this rigorous rationalist should be a champion of surtitles, and of opera sung in a language the audience can understand. Who is the greatest composer he's ever worked with? "Britten. A perfect musician, and a genius in every respect. We had our rift, and I served my time as one of his 'corpses' - he was very easy to cross - but he was very generous about my conducting of his work."

And what does Mackerras find most ominous about the current musical scene? "The record industry's decline. The rising respect for pop. And this horrifyingly philistine government. I expected great things of New Labour."

Mackerras is currently plagued by a shoulder injury caused by two interval-less Flying Dutchmen plus a Meistersinger on the trot, but his diary is full. He's conducting operas galore, recording Mozart concertos with Brendel, presenting Sullivan at a Prom, and doing yet more Janacek with his beloved Czech Phil. The RPS gong is well earned.