Sir Michael Tippett, unarguably one of this country's very greatest composers, died last week at the age of 93. Tonight, BBC Radio 3 is dedicating its entire evening schedule to his memory. Here, Andrew Green canvasses the recollections of a few of the composer's many friends and colleagues.

It had been clear for some time that Michael Tippett's life was ebbing away, yet when it came, his death almost sneakily caught a string of his closest musical friends and champions out of the country. A nice touch from a man renowned for his wicked sense of humour. From San Francisco, the conductor Richard Hickox described him as "... the most charming, witty and funny of men. I adored him." Speaking before a Sydney Festival concert on Saturday, Peter Cropper of the Lindsay String Quartet (who premiered the composer's two last works in this medium) said that they would be "publicly dedicating the occasion to Tippett's memory".

In London, meanwhile, the pianist Paul Crossley went straight to the piano on hearing of Tippett's death and played straight through the first of the two sonatas the composer wrote for him. Nothing sentimental in that, he insists. "What else could I do? My fingers expressed what I felt. But there was no reason to be sad - I loved it. He won't disappear."

Few know better than Crossley how the act of composition could consume Tippett. "When I asked him in my twenties for a sonata, he was keen to write something simple after tackling the huge Third Symphony. But what I received was something difficult almost beyond belief... and an outpouring of violent emotion. It was a little the same with the next sonata, intended to be just a set of bagatelles!"

On the other hand, Tippett's disciplined planning of many large-scale projects was meticulous almost to the point of obsession. "He had an iron will... an amazing inner strength," says fellow composer Steve Martland, Sir Michael's junior by all of 54 years. "We'd go for walks during which he'd stand still for absolutely ages thinking something through. He had this incredible ability to concentrate... as if he'd been taken over."

Despite this, Tippett's scores often display the difficulty he had in notating his music in ways that conveyed what he wanted or simply made things easier to perform. As if to compensate, he was readily philosophical when musicians suggested certain passages were just too demanding. "I remember singing in a Chicago performance of his Third Symphony in the 1970s, which he conducted," says soprano Heather Harper. "There's a section in the last movement where I just couldn't get the words through... it was so fast, rather `unvocal'... very tricky indeed. I said I was having problems and he just said, `OK change the notes then!'."

Honest attempts at tackling the near-impossible were met by Tippett with a childlike gratitude. During rehearsals for a Kent Opera performance of his second opera, King Priam, conductor Roger Norrington was determined to deliver a passage for the violins which had utterly defeated two leading orchestras in previous performances. "It's such wild, hysterical music," says Sir Roger, "but we recklessly decided we'd play it as written. Michael was there at a rehearsal and was so thrilled that he came striding across the seats from the back of the auditorium shouting, `Absolutely marvellous! It doesn't have to be right, you know!'."

"It was the mood of his music that mattered to Michael," says Richard Hickox, who has just recorded the complete cycle of the composer's symphonic works for Chandos, "... the message and atmosphere. He wasn't fastidious about detail in the way that Britten was." The conductor Nicholas Cleobury recalls having problems with the Fantasia Concertante on a Theme of Corelli during a Scottish Chamber Orchestra tour with Sir Michael in tow. "I asked him to talk to the orchestra about it. Out came those expansive, gauche gestures... but somehow the music's architecture came through, and the feel for what was bubbling away within it." Peter Cropper describes the day the Lindsays played the Fifth Quartet to Tippett for the first time as "simply the greatest of my life. There he was, 3ft away... and by the tiniest gestures - an eyebrow here and there - you knew exactly what he wanted."

Music could consume Tippett, but it didn't ultimately possess him. For 20 years Paul Crossley talked with him nightly, at length, usually on the phone. "He had this insatiable curiosity, but not just about musical things. He was passionately, violently concerned with what was going on in the world." But this concern, rooted in the experience of living through two world wars, never erased the innocent side to his personality. "When the quartet went to play to him," says Peter Cropper, "he'd sit on this vast sofa. When he laughed he'd throw his feet back over his head to touch the wall behind! He always had the energy of a 10-year-old boy."

"He was a complex man," says Steve Martland, "... urbane and sophisticated, and yet innocent in his hope and belief that his music really could help heal the world. And that music is saturated in generosity of spirit... that's why often there are so many notes!" Some, like Martland, have found that Tippett's visionary, complex music renders much of Benjamin Britten's output shallow in comparison. Others, like Sir Roger Norrington, see the two as complementary. "Ben could write something out brilliantly on the back of an envelope. A similar task might take Tippett a week, but it would be more thought-out - and the odds are that there'd be a message or idea coming through, possibly strange and mystical, that Britten wouldn't have addressed."

Tippett travelled the world to hear his music performed, but never in a proprietorial spirit. He was particularly thrilled, says Richard Hickox, with the interest taken by younger conductors. "He said that so much of his music hadn't been properly performed until conductors of my generation came along with their experience of the early music revival - especially Purcell and Monteverdi. They were his inspiration, and he wanted his music to possess their lightness and airiness."

According to his friend and assistant Meirion Bowen, Tippett always had a problem in listening to the music of other composers for pleasure - not out of a sense of his own importance, "... but because he could only react as a composer... he was always thinking what he might have done. But when he was forced to stop composing he discovered - only recently - a new sense of enjoyment in listening to music for its own sake which he hadn't had for years. It meant a lot to him."

Radio 3's tribute to Sir Michael Tippett tonight, 7.30pm to 12.30am