'I can see you from my bathroom window," the Duke of Edinburgh told David Bartlett, BAA's design director, when he came to visit the construction site of Heathrow airport's £4.3bn terminal five. "And, we can see you," replied Bartlett. From the vast new terminal's drop-off point, sited at the very west of Heathrow and overlooking the green belt of the Colne valley, you do indeed get a fine view of Windsor Castle. With all the latest security gizmos installed in T5, BAA snoops can probably tell you what make of toothpaste the Duke brushes with.
The Queen opened the first permanent building here in 1955. In typically British fashion, the airport had already been open for civilian passenger traffic for nine years. There had been no architecture at Heathrow then, just a village, or flying circus, of army surplus tents, caravans, marquees, corrugated hangars, and a lonely three-storey brick control tower.
If nine years seemed a long time even in the age of austerity, it has taken twice as long to build T5 in the era of instant everything - it was in 1989 that the Richard Rogers Partnership won the competition to be lead designers for the project, which is exclusively for the use of British Airways. This, I suppose, is what you might call long-haul architecture. The first flight, from Hong Kong, lumbers down to dock here on March 27. The big question is: has it been worth the wait? Twenty thousand building workers have come and gone since construction began in 2001. The only man still around to tell the tale from the distant days of 1982, when T5 was first mooted, is Mike Davies, the architect in charge of the project from beginning to end.
Without doubt, what you see at Heathrow, after so many years, is very impressive indeed, an architectural and engineering tour de force that raises the standards of British airport design by 100%. T5 exists in a design airstream thousands of feet above that of the rest of the sprawling and much derided Heathrow estate, and puts its cluttered and neglected precursor, the once revelatory Foster-designed terminal at London Stansted airport, in the shade.
Passengers step into one of the most breathtaking man-made spaces in modern Britain. Entering the huge check-in hall, you can see not just up to the heights of a mighty, white steel-truss roof, interspersed with generous bands of fretted glass, but from one end of the new, light-filled five-storey building to the other. Terminal five is 40m high, 176m wide and 396m long. It is so vast, says Davies, that you could slide three Empire State buildings, on their sides, into the luggage retrieval hall alone. Or two and a half Pompidou Centres.
Just look at it. A parade of 22 mighty white steel "trees" supports the massive roof trusses along the quarter-mile length of the terminal. It's like the biggest and most perfect set of Meccano a grown architect could ever have been given to play with. Floors are gleaming marble and polished timber. Walls are lined with opaque glass panels. There's not a fluorescent light fitting to spoil the view. High ceilings. Clear signing. All but invisible air-conditioning units. A cool and, for Rogers, remarkably restrained colour scheme, principally grey and white, with flecks of Yves Klein blue. Giant windows all round, and svelte, leather-covered seating designed by Foster and Partners, architects of the up-and-coming Heathrow East, a £1.5bn scheme to replace terminal two and the Queen's Building with architecture of the same standard as T5 in time for the 2012 London Olympics.
On one level, this is all quite remarkable. In pure architectural and engineering terms, it calls to mind some of the greatest structures of the past 150 years, all of them favourites of Davies'. "I don't really dare to make the comparison, but I like to think that we've been inspired and challenged by, well, Barlow's train-shed at St Pancras, the Galeries des Machines built for the 1889 Paris World Fair and Eiffel and Koechlin's Garabit Viaduct in the Massif Central. Oh, and of course, we've all been influenced one way or another by Stansted."
And what you see under this great roof is only the tip of an architectural iceberg. An underground transit system whizzes passengers to the first of two T5 satellites. One is complete, the second due for completion in 2011; miniature, stripped-down replicas of T5, both are longer than terminal four. Also below ground, but lit by an ETFE roof - the same translucent material as the bubble-like covering of the domes of the Eden Centre in Cornwall - are the six platforms of the Piccadilly Line, Heathrow Express and a future main line running west from Heathrow. A concrete outbuilding houses the heat-exchange wizardry that recycles waste hot air from elsewhere in the airport to heat T5. In its own ambitious terms, the building is probably as "green" as it can be.
A concrete ramp will eventually guide four-seat, electrically powered "pods" from T5's long-term car park to the check-in hall. A sweeping new road connects T5 directly to the M25. And you can just make out the two new channels created to reroute two rivers. This project alone cost £74m, and took 18 months. The twin channels are lined with reclaimed timber and are home to dace, roach, pike, perch, chub, shrimp, snails, nymphs and mussels trapped in the river Colne.
The sight of the green belt stretching west is also a reminder of the tight planning restrictions placed on the development. This is why the building is five floors high rather than the initially proposed two. It seems odd to say, but T5 is a compact design - compact, that is, for what it is required to do. And, here, I can't help thinking, is the rub. For all its architectural and engineering magnificence, T5 is so big because of the odd way we, the British, have decided to manage our airports.
Privatised in 1987, unlike the majority of its European rivals, BAA has to run along strictly commercial lines. To keep landing taxes, and thus fares, low and air-traffic heading this way high, BAA has turned its airports, and notably Heathrow, into gigantic shopping malls. In T5, among the 144 smart retail outlets and restaurants - there is no McDonald's, no stench of fast food - flyers will find a branch of Paul Smith and eating places that stretch the pocket from Cafe Costa to Gordon Ramsey's Plane Food. Good or bad, the need for all these shops, restaurants and executive lounges demands huge buildings with long walks from check-in to departure and equally long treks from arrival to exit.
If we were to organise our airports along different, less ruthlessly commercial lines, then surely they could be smaller and easier to navigate than these ersatz-shopping-mall behemoths, and in need of far less land and energy to shape and sustain them. The new MP2 (Marseilles-Provence terminal two) serving the French Riviera does indeed suggests an alternative to the notionally glamorous example of T5. Designed and built to serve no-frills airlines, MP2 is essentially a revamped cargo shed. Passengers carry their own bags and walk to the aircraft. Services are kept to a minimum. Who really needs more than a straightforward cafe-bar, a newsagent and clean lavatories? MP2 has cost a little over £12.5m. Why not go back to the tents, caravans and marquees of Heathrow 60 years ago? Heathrow served 60,000 passengers in its first year; it will process more than 67 million in 2008, so the scale of operations militates against a low-security canvas city.
Something, though, will have to give as fuel prices soar, as concerns for the environment grow, and we, grudgingly, question our reasons for flying so cheaply. Will there really be a third runway and a terminal six at Heathrow? Even if we stopped flying altogether, though, T5 itself could be reused. Every last bit of airport equipment, all those shops, restaurants, lounges, baggage-handling areas, customs posts, passport controls, the lot, could be lifted out of the building, leaving the stunning, land-bound, quarter-mile steel and glass silver machine standing, gleaming and ready for a new and, possibly, more responsible use. And the Duke of Edinburgh's successor would still be able to see it from his, or her, bathroom window.