In the company of explorers.

Shared ideals, individual styles and a sense of exploration and optimism continue to define the practice's approach to its work.

Waiting in the reception of the Grimshaw office one day, I find myself looking at a photograph in a book. The photo is of the entire NGP staff in January 1988, and it is in the twin-volume 'Product and Process' set, complete with stippled polycarbonate slipcase, designed by Jan Kaplicky of Future Systems to go with an RIBA exhibition of the same title. The architects in the picture cluster convivially around the top of the staircase: there are 28 of them in all. All but five of the men have put on ties for the occasion: Nick Grimshaw is proprietorial in a double-breasted light grey suit, though he defies the structure of the garment by leaving it unbuttoned. The biggest job in the office just then was the Financial Times printworks, valued at [pound]18.3m. Although the practice had previously worked in France and Switzerland, all the live projects were in the UK.

Neven Sidor as relaxed and tieless as he was in the 1988 photo, comes over and studies it Pointing out one fresh young face after another, he remarks that nearly all of those who subsequently left the studio did so to set up their own practices. Of those who stayed, four -- David Harriss, Chris Nash, Andrew Whalley and himself -- are now fellow directors with Grimshaw.

The advance copy of the latest Phaidon book on Nicholas Grimshaw & Partners, Equilibrium has just arrived. There is a whole-office photo in that, too, The top of the staircase does not suffice any more. The picture has to be taken from the street outside. The architects spill out of every window of the building, fill the pavement and block the road. There are around 100 of them: more are away on business, David Harriss is now apparently the only man wearing a tie. Nick's proprietorial suit has become a great deal more casual. Most of the faces in the picture are, again, amazingly youthful. It turns out that the average age of the office, including Nick and his fellow directors, is 31. The largest single project in the office is Zurich Airport at [pound]205m and there are others approaching that scale.

The commissions now come in from all over the world, including the United States. In the UK, no other firm of architects has been entrusted with so many landmark Millennium projects. In the capital it is in the thick of things, in the early stages of two of the largest and most sensitive urban projects of all: the remaking of Battersea Power Station as a cultural and retail venue, and the spectacular, large-scale expansion of Brunels Paddington Station. The difference between the 1988 practice and the 2000 practice is, therefore, immense.

Although Nick is chairman of the board, today things are consciously more democratic. The four other directors run individual projects, share ideals but bring their personal styles to the table. Moreover, NGP is being restructured along the lines of co-operative ownership. Eventually half of the shares in the business will be owned by the directors and half by an employee benefit trust. The effect is that nobody else can buy the firm, nor can it be broken up or floated on the stock market So there is no conflict between client and shareholders, and no relentless pressure to take on all the work that is available. NGP is free to turn down work that does not accord with its own standards.

The five directors tend to single out different aspects of the practice when asked to define its approach. David Harriss talks of honesty, an architecture that is self-explanatory Chris Nash also speaks of buildings being understandable, but adds that one must always ask Is it beautiful'? For Neven Sidor, it is important that the practice should start each project totally fresh, never applying a formula. He describes his ideal as: A team of designers following a rational chain of decisions, through magical territories unfettered by preconceived ideas, until they arrive at a destination that they themselves find surprising.' In this he is echoed by Andrew Whalley. Everything must be questioned from first principles, says Whalley Even their own competition-winning schemes must be subject to extreme scrutiny There is no house style, he says, only a 'shared approach'. This approach is hammered out at design review meetings where everybody pitches in: it is not an office where partners run projects without refere nce to each other. Nor is it an office where a culture of extreme deference to the boss prevails: the Grimshaw directors are among the most individually-minded you are likely to meet Though as Grimshaw himself observes, he has the longest experience of arguing a case.

For Grimshaw, it always comes down to how the building is made. The longest discussions concern details, At the beginning, he says, he and his colleagues would sit down and argue about the relative sizes of a bolt-head and its washer You get the impression that not only do such discussions still take place, but that they are actively enjoyed. Get the bones of a building right, he says, and it matters little how often it changes its use or grows a new skin.

The relative youth of the office -- younger on average, in fact, than many a start-up practice -- makes it something of a training-ground for each new generation. It is true that many go on to form their own practices rather than seek more conventional employment elsewhere: true also that the links tend to be maintained. Grimshaw is, for instance, collaborating on a house in Germany with a young practice, Bryden Wood, which sprang from the NGP stable, Similarly the industrial design section of the firm is treated as a separate enterprise, with separate premises, free to work on its own commissions.

The aim must surely be to keep alive the sense of exploration, of opening doors to new possibilities. To do this requires youthful blue-sky enthusiasm and optimism. To tackle large and complex projects however also requires enormous experience of the act of building. Few firms of architects manage to balance these forces with quite the elan of Nicholas Grimshaw & Partners.