Last year the Scottish Chamber Orchestra announced that 32-year-old Martin Suckling is to be their new associate composer. The orchestra had already given the first and second performances of Suckling's shimmering storm, rose, tiger; in February they premiere a major new commission called Six Speechless Songs to mark their 40th anniversary. Beyond that there's already a promise of at least three further collaborations, including a piano concerto for Tom Poster.

For those who already knew Suckling's music - especially for SCO audiences who had heard the orchestra perform storm, rose, tiger - the announcement will have come as no particular surprise. Suckling is among the most competent, most discerning and at the same time most listenable-to young composers currently writing in the UK.

Open any one of his scores and you'll find music that is impeccably constructed and intellectually vigorous. Yet his soundworld is also anchored in a language that's earthy and openly emotional. In conversation Suckling uses words like "tune" and "chord changes" to describe his music: he knows the power of simple, good-quality ingredients and doesn't feel the need to prove anything by complicating them for the sheer point of it. And it's this combination - ferocious intellect, emotional honesty, uncluttered delivery - that makes his voice so worth hearing.

There's something refreshingly unguarded about Suckling's scores. For example, when he writes folk harmonies or fiddle inflections for an orchestral string section, it's just his own musical heritage filtering through. He grew up in Glasgow and played fiddle in a ceilidh band while he was at school (one of his bandmates was Rory Macdonald, now Scotland's finest young conductor).

As a classical violinist Suckling was a rare talent (he could have easily pursued a career as a violinist) and his string writing reflects that, too: you'll never find him awkwardly grafting an abstract concept onto an instrumental line. When he composes he tries out his ideas on the violin or the piano or simply sings them out loud. "I try to write music that I would enjoy playing and I would enjoy listening to," he says, so it's not surprising that there's such a visceral quality, a realness, to the results.

I meet Suckling at his red-brick terrace house in south Manchester where he lives with his wife Hilary, a pianist and staff accompanist at Chetham's School of Music, and their five-month-old daughter Eleanor. Cheerful baby paraphernalia is scattered around the living room between the grand piano and the stacks of sheet music. Over lunch Martin and Hilary chat to me about the demands of new parenting. Today they're feeling in good shape, they say; the previous night Eleanor slept through until the morning for the first time since she was born.

For anyone who pictures the life of a composer in the Romantic archetype - the stormy, self-absorbed, possibly slightly impracticable artist - five minutes with Suckling should shake the stereotype for good. This is a guy who commutes to York University four days a week to lecture to undergraduates on contemporary music. He's up at 4.45am, back in the house around 8pm. It's a schedule that would break the hardiest of men, but Suckling remains positive about the job. The students constantly challenge him, he says, and the department is full of other interesting composers to share ideas with.

Not only that, the teaching material keeps him on his toes. At the moment he's focusing on spectral music; tomorrow's lecture is about the French-Romanian composer Radulescu. "It all filters through into my music," he says. "For example, I'm sure I wouldn't have written a piece like Release" - the kaleidoscopic orchestral score premiered by the BBC Scottish Symphony Orchestra at Tectonics last May - "if I hadn't been teaching a course on spectral music at the time."

The problem, of course, is time. Suckling composes at night or at weekends after putting Eleanor to bed. Sometimes he manages to fit in a few concentrated minutes in his office at York, between lectures and students knocking on his door for advice. So it's little wonder that his commission for the SCO's 40th was a wee bit tricky to get off the ground.

"I really felt the pressure on this one," he says. "I'd just been appointed associate composer. It's a big anniversary. My piece will open the programme and it's sitting next to Chopin's Second Piano Concerto and Beethoven Five. Nobody's going to come off particularly well with all of that in their head."

The SCO left most of the creative parameters up to Suckling, with just one caveat: that the music should feel somehow celebratory. And celebratory, says Suckling, is a lot trickier than it sounds.

"Writing upbeat, joyful music is way more difficult than writing dark and angsty music. Because as soon as you're using these sort of sounds" - he goes over to the piano and bangs out a series of bright major chords - "it's really easy to slip into the dreaded world of cheese. Whereas if you're doing something like this" - he plays some menacing, stormy clusters - "it's a lot easier to sound meaningful. At least superficially."

I know what he means, but Suckling doesn't exactly seem the stormy or menacing type. He had plenty of reason to feel celebratory while he was writing Six Speechless Songs: he'd been happily married for almost five years, his career was sky-rocketing, Eleanor had just been born. "True," he agrees, "and I suppose there is an aspect of new life in the piece, with all the energy that comes with it. The last movement is a berceuse" - he picks out a lilting, Brittenesque melody on the piano - "and the tune is one that I would sing to Eleanor to get her to sleep when she was tiny. So yeah,I guess that there are different types of celebration in thispiece. Hopefully without being too naff."

Naffness isn't a word I'd associate with him either. What does he mean by it? "It's a bit nebulous, but you definitely know it when you hear it," he ponders. "It also depends where you are. In the States my music was regarded as dangerously European. I used a fair amount of dissonance, I didn't sit on tonic pedals all day, I didn't write loads of rock-inspired stuff. Over there I'm almost old-fashionedly modernist. Whereas here I'm really, really not." He looks momentarily worried that he's been undiplomatic, then shrugs. Suckling seems remarkably levelheaded about the whole question of how his music is perceived. If he is prone to the usual creative insecurities, he doesn't have time to dwell on them at the moment.

Inevitably Six Speechless Songs did get off the ground, despite its initial teething problems. Choosing the right title really helped, says Suckling; he'd been working under the provisional title of Snail - "inspired by a brilliant bright-coloured Matisse painting" - but it got him nowhere. Then he changed tack and things began to roll smoothly. He settled on an extract from Shakespeare's Eighth Sonnet to provide the kick-start: "Mark how one string, sweet husband to another,/ Strikes each in each by mutual ordering,/ Resembling sire and child and happy mother,/ Who all in one, one pleasing note do sing;/ Whose speechless song, being many, seeming one,/ Sings this to thee: 'Thou single wilt prove none'."

"I like the idea of speechless song," he says. "I like the idea of many people singing one song; that fits with the image of both a family and an orchestra. The song theme fits my melodic impulse as a violinist. And after Release, which was all about big shifts of harmony, I wanted to write something that had proper polyphony. So the idea of many parts making one song seemed to make sense, too."

Suckling cautiously acknowledges that, yes, the finished product does, he thinks, fulfil the celebratory remit. "It's definitely the most overtly celebratory thing that I've ever written," he quickly qualifies. "But let's see how it works in context. I mean, whatever I've come up with, it'll never exactly outdo Beethoven Five, will it? However long I've held my big major triads, they'll never compete with Beethoven's C-major finale." Competing with the single most emphatic and iconic symphonic expression of light, triumph, hope and humanity? Possibly not, but Suckling isn't one to shirk a small challenge.

The Scottish Chamber Orchestra's 40th anniversary concerts are at the Usher Hall, Edinburgh, on Thursday and City Halls, Glasgow, on Friday. See for ticket details