The rave reviews from Edinburgh and overseas were right. Gregory Burke's play showing the venerable Black Watch under fire in Iraq and under threat at home is rich, exciting, humane and moving, and staged with dazzling virtuosity by John Tiffany. It's taken two years, and the conversion of the Barbican auditorium into a drill hall, for the National Theatre of Scotland¿s production to reach London. But it has, emphatically, been worth the wait.

In 2004, the 300-year-old Black Watch was deployed to unsafe, US-controlled northern Iraq even as Geoff Hoon planned to merge Scot-land's fiercely independent regiments. Burke's play flits from a fictionalised version of the interviews he conducted with young ex-squaddies in Fife, to their recollections of action, camaraderie, bereavement and banter. It's urgent and pacy, spoken in thickly evocative accents with more four-letter words than full stops. A good deal of regimental history is thrown in, as well as choreographed violence, song, video and even sign language, when the soldiers mutely read letters from home over swelling music. It shouldn't work as a whole, but it does. Gloriously.

Although the show's creators claim to have no political axe to grind, they regard the Iraq War as a reckless adventure - 'bullying' that wasted lives and sullied the reputation of the British soldier. But Burke demands, and earns, sympathy for the ambivalent pawns caught up in this unpopular conflict. They are boys brinking on manhood, from a place where soldiering is a dying industry and a birthright, but they scorn tradition almost as much as the idea that they are 'knuckle-drag-gers' who can't get another job. They love fighting, and they hate it. They are boorish, aggressive, touchy, desperate to boast or confide but furiously intolerant of civilian questions.

If you were looking to pick faults in this majestic piece, you could say it sometimes seems to regard valour, loyalty and thuggishness as equally demanding of respect. And it is arch at times, as when actors playing soldiers ask the actor playing the writer whether actors get laid a lot.

Nevermind. Burke and Tiffany are supremely well-served by a 10-strong cast that cannot only act, but also looks credibly fit, hard and potentially dangerous. Although it's an ensemble piece, it's hard not to single out Paul Rattray as Cammy, the former computer student who is effectively the audience's liaison with the squad.

Emun Elliot, too, gives a stand-out performance as the oafish Fraser that erases memories of his Dad's Army counterpart.

Praise is due, too, to designer Laura Hopkins, who can credibly turn a pub pool table into a Warrior armoured car, and to choreographer Steven Hoggett and musician Davey Anderson, whose brilliantly offbeat contributions make this piece even more forceful and emotionally resonant.

Until 26 July, box office 020 7638 8891 or www.barbican.org.uk