As Princess Diana’s coffin inched its way through the darkness of Westminster Abbey in 1997 it was to a slow lament – Song for Athene – that played to several billion TV viewers worldwide and propelled John Tavener from the marginal status of a distinguished classical composer to the purlieus of serious celebrity.

Audiences with no grounding in contemporary music sought him out and registered his eye-catching appearance: long hair parted in the middle, shirts unbuttoned to the navel, something between Jesus and a 1960s rock star. And for many he became almost a spiritual guide, known for the fact that like a latter-day Bach, his work was steeped in Christianity. Or, to be exact, a Christianity that reached beyond Bach to the liturgies of what he liked to call ‘primordial tradition’.

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As with most things about Tavener, his take on ‘primordial tradition’ was enigmatic, and attempts to pin him down were usually confounded by cloudy conversational allusions to St Dionysius the Areopagite, the Virgin Martyr Anysia or other obscure divines of Eastern Orthodoxy.

But then as now, there was a paradox governing his work. He once told me with some justification that he thought himself ‘rather radical’ to be writing new music that referenced the distant past; and part of his achievement has been that he does so without actual reproduction. A Tavener score may come with the title Diodia or Agraphon, but there’s no mistaking it for some ancient artefact in sound: it absorbs history but inhabits the present.

Another paradox is that the best of Tavener’s work has a profound simplicity that seems to speak great truths with a disarming innocence and absolute conviction – in perhaps the manner of the Russian Holy Fool, the yurodivy, who turns up in opera telling the Tsars their fate. And Tavener’s convictions have been constant, even when they didn’t obviously look it.

Born into a family of north London builders – ‘grand ones’, he explains, ‘mansions and palaces, not changing taps’ – his background wasn’t exactly ascetic. And he first came to attention on the secular terms of a noisily iconoclastic entertainment called The Whale that premiered in 1968, attracted the Beatles who recorded it on their new Apple label, and shot the young Tavener into fashionably swinging circles where he acquired the taste for those unbuttoned shirts.

But much of his childhood was spent playing the organ: either in the chapel of Highgate School where he was contemporary with another notable composer of choral works, John Rutter, or in a Presbysterian church in Hampstead. Religion featured in his music from the start – even The Whale was based on the Bible story of Jonah. And finding his way a few years later to the Eastern Orthodox faith concentrated these youthful leanings into an artistic identity.

With the zeal of a convert he became, as he now says, ‘dramatically’ Orthodox, mirroring the stark, sluggish severity and tonal structures of ancient liturgy in his scores. And being slow, spare and repetitive they earned him the affectionately mocking label Holy Minimalist – a term that survivors of his not-so-minimal three-hour Resurrection or seven-hour Veil of the Temple might feel qualified to challenge.

But these works were not for entertainment. They were ‘icons’: musical correlatives of timeless, emotionally impassive Byzantine portraiture, conceived as aids to prayer and windows on a world beyond. Dismissing the idea of progress as meaningless, he argued that as art had reached perfection in primordial times, so everything the modern West produced, even the spiritually motivated West of Bach and Bruckner, was in error.

He morphed into a cultural Ayatollah: popular with the public who were pleased to find a ‘serious’ composer writing music they could absorb, but isolated among his professional peers. ‘It bothers me,’ he said, ‘that I don’t… have any composer friends. It would be nice if I did.’ But with time, he decided that he wasn’t born to be an Ayatollah. Musically and mentally, horizons opened to the point where he recognised primordial tradition as ‘a sort of tyranny… I felt the need, in my music at least, to take in other colours, other languages.’

It was a gradual process in which his devotion to the East as the source of God-centred art began to absorb elements of Hinduism, Islam, even Shamanism. And sitting in the Dorset village farmhouse where he lives – what would be a classic country existence but that his barn is now a Greek Orthodox chapel – he would talk in a matter-of-fact way about mystical encounters with Apache medicine men (how from one he had got a pow-wow drum for use in The Veil) and visitations from the spirit of a dead philosopher who told him, in two words, to loosen up. Open his ears to wider possibilities.

A more straightforward reading might just be that here was a composer in his sixties softening with age; and when I once suggested this, he smiled and said ‘it’s possible’. During his hard-line years he faced successive crises: serious illness, serious drinking, serious demons. Now his life was settled, brought to order by a no-nonsense, younger wife and the arrival of a third child. ‘I’ve become a peaceful family man,’ he said. ‘It helps.’

But whatever the reason, he was no longer ‘dramatically’ Orthodox or anti-Western. He now listened to Bach with pleasure. He played it on the organ of the church next-door in Dorset and happily explained it was here that Arthur Sullivan composed ‘Onward Christian Soldiers’. As for primordial tradition – ‘Well, it’s important, but you have to find a way of honouring it that communicates with modern man. Now I feel free to wander further, so long as it makes metaphysical sense.’

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Tavener’s wandering took him into controversial territories, not least the Koran which provided the entire text of The Beautiful Names, a grandly spacious work for choir and orchestra that meditates for an hour and half on the 99 names of Allah and prompted ‘Tavener goes Muslim’ headlines in the British press when it premiered (with airport-style security procedures on the door) at Westminster Cathedral in 2007.

It was an event that showed religion at its worst, with fundamentalist Christians protesting against the piece being done in a church, Muslims (who don’t much care for music in worship) threatening hostility, and Tavener faced with the charge of opportunism. It was, he admitted, a can of worms.

But it was also a conspicuous platform for the pow-wow drum, struck ceremonially every 99 beats through the score (one beat for every name); and by now the drum was a familiar feature of his sound world, turning up in the Mass of the Immaculate Conception that premiered in Zurich in December 2007 and surprised its audience with invocations to Hindu goddesses inserted into the Latin text. ‘A bit of a stir’ was Tavener’s prediction.

What he couldn’t predict was the catastrophe waiting to happen on that Zurich trip. Always plagued by frail health, with an inherited cardio-vascular condition, Marfan syndrome, he suffered the first of two heart attacks that left him close to death and physically devastated.

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Since then he’s written almost nothing, but his habit of stockpiling scores well in advance of a commission has meant that several unheard pieces have now appeared. And the irony is that they include two contemplations of death: a chamber work, Towards Silence, and a universalist Requiem that premiered last year in Liverpool and ends with a musical gesture that, he says, symbolises ‘the glory of ceasing to exist, of extiguishing the fake self and allowing the true self to shine forth’.

It’s an idea of death as achievement rather than defeat. And if, as may be the case, it proves the last big work he manages to complete, it will at least be an appropriate culminationto the career of someone who has seen himself as, in his words, a ‘sacred artist’. Listening for the eternal in the transient. Meditating on mysteries. Waiting on God.

Michael White