Never meet your heroes, they say. But if you grew up with classical music in the 1980s, there was fat chance of that. Stravinsky, Britten, Shostakovich, Walton: you’d just missed them. Which is why, in 2001, and finding myself duty-managing an 80th birthday concert for Sir Malcolm Arnold, I inched past his minders and delivered a few trite, polite but entirely sincere words of gratitude and admiration. No response: Sir Malcolm stared blankly ahead. Then he gripped my hand, and started shaking. And kept shaking, faster and faster, his grip tightening like a vice. Raising his head slightly, and pumping my hand with increasing force, he growled: ‘I’m not letting go until you call me Sir.’

In truth, it was reasonably widely known by then that Arnold was no longer ‘all there’. Orchestral players loved to embroider his drunken antics; this, after all, was the man who’d shouted ‘bollocks!’ at Sir Malcolm Sargent. Still, easier to excuse him as an eccentric — what a terrific old boy! — than admit that we were honouring the traumatised wreckage of the man who wrote such vital music. One read about Schumann or Hugo Wolf, reassured that tortured geniuses were a purely historic phenomenon. The story that emerged after Arnold’s death in 2006 — the depression, the suicide attempts, the repeated breakdowns and the brutal therapy that had scoured out and finally erased his glorious creative gift — is still barely fathomable.

Because, damn it all, his music is just so life-affirming! Arnold writes melodies that sound like you’ve been humming them since childhood (just mentioning his score for the 1961 film Whistle Down the Wind is enough to guarantee that its main theme will be lodged in the ear all week). More than that, he has style: a streamlined, bracing New Elizabethan optimism. Fanfares rocket upwards in fourths, like sonic Skylons. Banks of dissonant brass paint black John Piper cloudscapes, and violins soar clear into cool blue skies. Even at the bleakest moments (and Arnold’s nine symphonies are what we might have heard if Shostakovich had chronicled post-Suez Britain), there’s a readiness to make mischief. A dignified melody suddenly gives a little skip, and you see Sir Malcolm placing one finger slyly by his nose.

‘We don’t talk about the life,’ Paul Harris told me. He’s Arnold’s biographer and director of the annual Malcolm Arnold Festival, which has been held since 2006 in the composer’s birthplace of Northampton. Over a single busy weekend it generally runs to at least one professional orchestral concert; the rest of the programme is filled out by amateurs, enthusiasts and a substantial dose of civic pride. That grassroots healthiness is itself a tribute to Arnold’s peculiar qualities. It’s hard to imagine the formula working quite as well with either of Northampton’s other great 20th-century symphonists, William Alwyn or Edmund Rubbra.

All musicians, amateur or pro, love music that makes them sound good, and Arnold makes them gleam. The gala concert this year came from the BBC Concert Orchestra under Barry Wordsworth, and I’ve rarely heard them sound quite so on-point. Arnold’s Second Symphony dates from the year of the coronation. It opens with a melody that feels like sunlight spreading across a landscape, but what came out most strikingly at the Derngate was the purity of Arnold’s writing: the concentrated power of the brass, the eloquence with which the woodwinds knot and untangle the symphonic thread. Playing some 20th-century scores can feel like wading through sludge. Arnold never miscalculates a sonority, and each splash of harp or muted horn chimed out as vividly as the trumpets that crowned the skyscraping final peroration.

The previous night, at St Matthew’s Church, the amateur Northampton Symphony Orchestra had played one of Arnold’s most familiar works, the Ivesian Peterloo overture. The qualification ‘amateur’ wouldn’t have bothered Arnold, and it was irrelevant here: the NSO played with a polish and a focus that’s more common than critics tend to imagine among the UK’s non-professional ensembles. Later, John Gibbons conducted Stolen Face, one of the so-called ‘Denham Concertos’ beloved of the postwar British film industry. Arnold begins as ersatz-Rachmaninov before sliding, characteristically, into a suave lopsided waltz, elegantly handled by the pianist Rhythmie Wong.

And then came the Variations on a Theme of Ruth Gipps of 1977: a tribute to an old friend from a man facing absolute darkness. Even here the clarity, the craftmanship, even the humour, glint beneath an overcast surface. The NSO’s oboes played their long, yearning melodies as if in a single breath. To paraphrase Hans Sachs, to come through spring, summer, autumn and winter, through all life’s suffering and sorrow, and still sing a beautiful song — that is what we call a Master. Malcolm Arnold said only that he wanted to be remembered as ‘an honest composer’. I don’t think he was capable of being anything else.