David measures up to his new Goliath

Fifteen years a superstar, always exciting and innovative, Mach currently has eight sculpture shows around the world, from a huge popular success in Tel Aviv to Goodwood and London's Royal Academy. His output is phenomenal, his list of shows running to five pages - Moscow, Sao Paulo, Geneva, Tokyo, Milton Keynes, Paris, to New York.

Now the big one - literally. Mach's latest extravaganza is his first-ever permanent work and the largest single sculpture to be built in this country: a massive 140ft long, 22ft high, and constructed from 181,754 bricks at a cost of almost #700,000. This vast impressive structure runs alongside the A66 on land which was originally part of the famous Darlington-Stockton railway, where George Stephenson actually drove the first steam train in 1825.

''This is where trains were born and where an engineering heritage was forged. This is where people had ideas and the skill and imagination to realise them,'' says Mach, oozing the same kind of commitment, enthusiasm, and imagination that made Stephenson famous.

Trains should move. Mach's new sculpture is set in stone - well bricks, actually. Was it tongue in cheek? ''Oh no, art imitates life,'' he says, and true enough the GNER train I went on, as often, broke down making a nightmare eight-hour journey from Glasgow.

So was the trip worth it? The taxi driver who took me from Darlington station thought not. But, said the driver, it's better than Gateshead's angel. Both are being achieved with lots of lottery money.

Mach's train has been a long time in gestation. The idea originated in his degree show in 1982 with Running Out of Steam, a structure hurtling forward as though emerging from its own smoke. ''I made it from magazines. Even then I visualised it in brick. I was in Wales, standing at the bottom of a hill with a brick tunnel and a row of brick terrace houses on top. I thought, I want to build all that. I'm halfway there now! It's great.''

The Darlington train didn't emerge fully-fledged, though. It started small and has taken two and a half years to grow. Morrisons Supermarkets originally wanted a #40,000 sculpture but listened to Mach's grandiose idea and were hooked.

Creating this art monster required a computer, says Mach. ''It took months to log each Accrington Nori brick. Simon Lawson of Fletcher Joseph Architects keyed them in, every 181,754 last one. I always build everything myself, but this was impossible. However, I wasn't prepared to hand over a job not knowing where every single brick went. And I did. I actually stood there and said: ''Take that brick off, it's wrong.''

Shepherds's Bricklayers got hooked too. ''They were supposed to be on a rota, but refused to budge. They loved it and developed a passion. They've built a magnificent sculpture. Passion is a source of energy and produces something better than you imagined.''

Born in 1956 in Methil, Fife, to a Polish refugee father and a Scots mother, Mach's training began at Dundee's college of art. Next came London's Royal College from 1979-82, ''a good time to be there''.

He met his wife, Les, at school, they married in 1980, and have worked side by side ever since. Les made the 20ft train model with Simon Phipps and Jane Turner, who often work on the Machs' projects. ''It's like a wedding cake, amazing. A vision,'' says Mach.

''I miscalculated. It took over three months to make, and cost a bomb. Every brick was hand-made from MDF, mortar carefully applied.'' He's right. The model, on show at Darlington, is superb.

Mach is currently showing impressive Train collages in London at Jill George Gallery. He's also making a giant 450ft x 10ft collage, titled The Revellers, for Melbourne International Festival this autumn.

The work goes down a street and round the corner and the problem of scale is being solved by using billboard posters rather than magazines as raw material.

''I want a herd of kangaroos, nudists, musicians, and a fantastic skyline.'' Collage is Mach's new passion. ''You can make

it political, use contemporary social comment. Because these are real people who exist, every time you cut you bring something to it - like chopping off Castro's cigar and putting it in a peasant's mouth.''

Mach has a 12-year library of files of pictures - people looking left, women looking right. ''We even have a collection of people riding rhinos.'' He uses backgrounds from Monet and skies by Turner, and plans a whole series of storm pictures with ''stuff flying all over the place. All that art history. I just love that''.

Is this surreal collage? ''Absolutely not. Surreal is too bloody easy. These people exist. That roots it in fact, not fiction. I find the image, cut and compose. I can have a cast of thousands - Cecil B De Mille stuff. Now I've finished the train I'm hot on these collages.''

Meanwhile, Mach laments lost opportunities in Scotland. ''I'd like to do a big show there, but nothing happens.''

His paper Parthenon for Glasgow in 1990 was ironically entitled Here To Stay, but did nothing of the sort. Likewise his 1994 Temple at Tyre at Leith. His latest plan is for a brick-fronted artists' club for

Glasgow's year as City of Architecture and Design in 1999.

''With 1999 Year of Architecture and Design on the horizon Glasgow should soon become the place it's always pretended to be: an artistic hub. My idea is for a real international arts club in the city centre.

''I've already made drawings and models for the building, also in brick. Its five big brick columns bulge, as though I've taken a normal facade and squeezed it to reflect the power house of ideas within; a place bursting with goodies.'' It is hard to see signs of his enthusiasm being matched by Scotland's recognition of its own. Even

the Scottish National Portrait Gallery's snail's-pace acquisition of Mach's four collage photos of sports stars Alex Ferguson, Gavin Hastings, Yvonne Murray, and Stephen Hendry has not been trumpeted around.

Perhaps Mach will have better luck with his portrait head of Nelson Mandela. Mach is keen to make it and supply five mini-versions for sale to raise funds of around #30,000 for Edinburgh's Refugee Centre (''My father, remember, was a refugee.'') But, he needs an initial #10,000 sponsorship to get started. Any offers?