The most mischievous thing I ever did when I sat on the RIBA Awards Committee was to manoeuvre the Tiree Shelter on to the Stirling Prize shortlist. I liked the idea that a £95,000 ferry shelter could rival Norman Foster's £100m British Museum Great Court. There was something about Sutherland Hussey's building that was intriguing. Its purity of line - no more than a pair of white walls ending in a glass box that framed and captured the wild landscape of this Romantic Scottish island - seemed magical. I loved the way the commonplace (a shelter against the wind while waiting for the local ferry) had been transformed, for a minimal budget, into the exceptional. This was architecture at its purest, and, as such, a worthy competitor for the Stirling. There was an added frisson: to assess it, the distinguished panel of judges would have to fit a tortuous excursion to one of the most inaccessible spots in the British Isles into their crowded schedule. To me, that was irresistible.
Sadly, the Tiree Shelter did not win. None of the shortlisted entries had a chance against Herzog & de Meuron's even more magical Laban Centre in Deptford. But in a different year, without a clear front-runner, it could have slipped through, for with the Stirling, as in all high-profile competitions, there is nothing inevitable about who wins. Fashion, sentimentality and the maverick opinions of the judges and even the shortlisters all play their part, as is clear looking back over the prize in the tenth year of its existence.
It is hard to remember quite what a ropy state British architecture was in when the Stirling Prize began in 1996. The profession was still picking itself up from years of recession, while the tidal waves of Lottery millions that subsequently transformed British architectural ambition were still a distant dream. In later years the winner, Stephen Hodder's Centenary Building at the University of Salford, would have been hard-pressed even to reach the shortlist. But for the newly launched competition it hit several buttons: the practice was young, media-savvy and northern. The decision gave out all the right noises about being open and forward-looking.
Since then, the Stirling has slowly crept into the national consciousness to the point where it has taken its place along-side those other hardy perennials, the Booker and Turner Prizes. With the help of Channel 4, it has attained a glamorous inevitability, and the sort of building that generally wins has changed. This is just as well: a diet of worthy northern buildings would never have sustained the Stirling.
So who has won and, looking back, were they the right winners? Certain sorts of building have always been doomed: specifically, private houses (too self-indulgent) and (other than one exceptional case) commercial buildings. Architects are still shot through with a certain moralism and remain uncomfortable with buildings celebrating capitalism. The ideal winner is still a public building. But moralism goes only so far. Architects are also seduced by glamour. Worthy buildings never win the Stirling, whether they be Bill Dunster's environment- ally friendly BedZED housing or BDP's innovative inner-city Hampden Gurney School. If you want worthy, follow the Prime Minister's Better Buildings Award.
Given the need for glamour, it is not surprising that judges have preferred the fashionable high-tech, where architecture meets engineering. These are easily comprehensible, graphically dramatic buildings, preferably reducible to a single-line drawing in the mind. Foster's Gherkin and his American Air Museum at Duxford, Lord's Media Centre from Future Systems, and Wilkinson Eyre's Millennium Bridge at Gateshead have all sailed through. By contrast, heavy, unfashionable architecture that needs careful analysis and digestion has never done well - one thinks of Benson & Forsyth's breath- taking encapsulation of the city in their Museum of Scotland or Caruso St John's intense New Art Gallery in Walsall.
Once, and only once, the judges went against form and ignored the slick high-tech image favoured by the public, architects and bookies alike. In 2001 they turned down Nicholas Grimshaw's Eden Project for Chris Wilkinson's steelworks-turned-science centre, Magna, in Rotherham. This was a real jaw-dropper on the night, but the right decision. The Eden Project was clever, but in its manipulation of space Magna was sublime, not a quality often found in modern architecture.
If visceral emotion perhaps swayed the Magna judges, sentimentality undoubtedly played its part with Lord's Media Centre from Future Systems. Architects still yearn to see themselves as modernist pioneers creating a form-breaking architecture by pushing at the boundaries of technology. Combine a space-age image, the exotic use of boat-building technology and the feel-good story of a small, highly principled but embattled firm that had been on the brink of collapse, and you hit all the right notes. That the building came in well over budget, forcing the client (Brian Thornton, chairman of the MCC Estates Committee) to resign, and that its highly crafted design smacks of the self-indulgence of the Arts and Crafts movement were pushed to one side.
Then there is the case, in true Booker style, of the right architect winning for the wrong building. Will Alsop should have won in 1997 for Le Grand Bleu in Marseilles, undoubtedly his best building, but he was beaten by Michael Wilford's Stuttgart Music School. In the end, Alsop won the award in 2000 for his quirky Peckham Library, an effervescent building that does much for its run-down neighbourhood, but which seems lightweight beside Le Grand Bleu. In a strong year, it was lucky to beat the Walsall Art Gallery, Marks Barfield's London Eye, Sauerbruch Hutton's GSW Building in Berlin and above all Foster's Canary Wharf Jubilee Line Underground station. With Tracey Emin as a judge that year, however, the quirky had a head start.
Even so, it is hard to believe that the Peckham Library beat Canary Wharf Station, and that none of the Jubilee Line stations ever won the Stirling. To my mind, the magisterial control of space at Canary Wharf, Alsop's shimmering- blue North Greenwich and Michael Hopkins's cavelike Westminster Stations remain the most exciting architecture of the past decade. I still get a thrill every time I use them. But I suppose they fall into the black hole of unfashionable heavy architecture. In 20 or 50 years' time, the fact that none of these three won will seem the strangest gap in the Stirling Prize list.
Not that this really matters. Though it sets out to be impartial, the Stirling inevitably ends up as a subjective choice, hardly surprising when buildings can be so completely different that it is often a choice between apples and pears. No wonder fashion, sentimentality and maverick personal opinion play such an important part. Yet the Stirling has done what matters. It has raised architecture's profile, inspired clients to demand that their architects come up with an award-winning design, and shown the range of exciting buildings British architecture can produce year after year. It all seems very different from 1996.
"The RIBA Stirling Prize: a celebration of British architecture" is now at the Architecture Gallery of the Victoria & Albert Museum, London SW7, until 16 October. The winner of the 2005 Stirling Prize will be announced on 15 October
Giles Worsley is architecture critic of the Daily Telegraph