Well, you could turn it into a dance hall. That's what Mecca did during the Second World War. Old photos of airmen and WACs in uniform, jiving in the auditorium, show that the place could swing. Or you could flood the stage with water and freeze it, so turning it into a skating rink. Rock'n'roll gigs could be held there with a greater intimacy than can be achieved at Wembley. No wonder that the engraver of the exquisite Dieu et mon Droit Royal coat of arms, high up on its new Portland stone facade, sensibly left off the name Royal Opera House above it. No one dares predict its name, let alone its future.
The House faces a major crisis. It has no artistic director, no music director, no programme and its staff has been halved from over 1000 to 526. It has also been asked to sign new, and even tougher terms. Wealthy patrons are threatening to pull out their millions, and 81 members of the Royal Ballet are threatening to bring down the curtains and carry on independently at Baron's Court, despite the fact that opera with ballet programmes are the best box-office draws.
But an opera house for ballet has been built as well, and it is one of the most up-to-date, in terms of technology and acoustics, in Europe. My bet is that it will be an opera house, which is probably why next Friday, Chris Smith will stage his "Creative Mapping" review of Government spending on the arts in the Design Council offices at Bow Street, which overlook the opera house. Creative accounting is what is called for in his review of the opera house: there is no more spectacular sinking fund in the arts than the opera house. The cost of pounds 214m includes the pounds 20m closure costs. The Arts Council lottery gave the opera house pounds 58.5m, plus pounds 20m for closures, which has been a financial disaster. Shops have been leased at pounds 250 per square foot all along its arcade, and patrons have paid for the rest to bring the cost of the building up to pounds 196m, which most people consider to be too much.
The Bastille opera house in Paris cost twice as much, at over pounds 400m, but President Mitterand just wrote a cheque to cover the amount. So is Pavarotti destined to perform for ever in the Park?
Dame Kiri Te Kanewa is already on record as saying that, with a full season and rival venues, the Royal Opera House badly needed more than a face-lift. Staying on would have signalled the long term decline of the place, which is why Jeremy Isaacs held a competition in 1983 to find the architects to rebuild the opera house. It was won by Edward Jones, with Jeremy Dixon. "This building is Jeremy Isaacs'," Edward Jones insists. "You only get good buildings with a good patron." Both architects miss him.
"Oh, it's a bespoke opera house, all right. And it will open on time and within budget by December next year." Edward Jones is adamant on this point, despite the fact that the big girders in the fly-tower didn't connect, which delayed things by up to two months.
As opera houses go, the building is positively Wagnerian in scale. Not artsy-craftsy "Meistersingers", but Valkyrie in stone and glass, anchored in a granite plinth. Agreeably bowed along its Bow Street elevations, you can see the skillful way in which a Victorian cast-iron glasshouse - the Floral Hall - has been restored and sandwiched delicately between the familiar stone portico and a new, narrow glass tower that houses the elevator.
In Covent Garden, which is always full of curiosities such as fire- eaters and clowns on stilts, the opera house gets more photocalls than the mime artist painted silver and doing Max Headroom impersonations outside it. Or the aboriginal didgeridoo player camped out in its arcades.
Edward Jones and Jeremy Dixon were refused permission from the Royal Opera House management to take me on site. So I'll have to take the architects word for it that they are democratising opera. Everyone enters through the front door and promenades through the building. Planners call that enjoyment "increased access". Just when opera is being seen as a strange hybrid that is both elitist and populist, the architects have sought to make everyone share the same entrances, stairs, bars and restaurants, and mingle, whatever you have paid for your ticket. Whether you stand in the Gods or sit in a stall, you will get there via the same routes as everybody else. The aptly named Crush Bar is no more.
Various styles, ages and uses of buildings, even on the same street, are united by workmanlike viewing platforms, balconies, walkways and clear- glass screens which expose what is going on inside the building. It is a pleasure to look at the shapely and disciplined building that results, "more of a town than a single building", Jeremy Dixon says.
At every point, the opera house confronts its neighbours with a stylistic flourish in the modern idiom. The cupola on the theatre museum that faces the opera house on the corner of Bow Street, is mirrored by a screen billboard which is set deep into a recess like a big, blue, Anish Kapoor canvas. Monumental apertures, some glazed, others screened, let you see what is going on within. It's in the spirit of Covent Garden, which is essentially one big, performing arts centre. Sensational by day, it will be even more sensational at night when its prismatic glazing and digital screens glow - and you can watch scenery shifts and performers crossing into the rehearsal rooms.
One fifth of the budget in the old opera house was spent on stage equipment. All scenery had to be man-handled, put on a dog-leg shift, and lifted. But now the new opera house has what all modern lyric theatres have: a computerised scenery system. A pantechnicon can roll into the lift and the built scenery be put on the pallet and kept intact. At the end of the performance, at the press of a button, it moves off in one piece into a huge area where it's kept until the season closes, before moving to storage in South Wales.
The stage in the afternoon is freed for more performances. So this massive fly-tower reminds us of a basic reality unique to opera - you never see the same one two nights running because the singer's voice gives out. Programming means two different operas in a week, ballets in between, and at least three or four rehearsals going on around the central productions.
Jeremy Dixon and Ed Jones are in good voice after 15 years, during which the brief and the budget changed as many times as the management. Vulnerable in working on a historic, listed site, and under public scrutiny, they enjoy the fact that everyone in Covent Garden is looking up at it and hope their building won't come to symbolise all that is wrong with the Royal Opera House management. "The building has a certain presence and an implied performance that is the force behind its architecture," they say. "If we're lucky, it could be the Phoenix."
Turn the corner into James Street, and again into Russell Street, and you see the street elevations that everyone from English Heritage to the Royal Fine Arts expressed an opinion on before the canvas was even primed. The results are better than the scale models. Neither hugely modern, nor redolent of Inigo Jones, the architects avoided pastiche with a witty geometry that reverses the classical order on a modernist grid. Windows are biggest at the top, moving down rhythmically to get smaller, trickling away above a forest of columns. Like all post- Modernists, they describe themselves as Mannerists to distance themselves from any superficiality. A leaner, fitter and much more subtle architecture emerges, but on a monumental scale.
Five hundred yards away at the National Portrait Gallery, the architects have been making their mark again, but on a smaller scale. On Monday, under a glazed roof, their light-filled little basement cafe and adjoining bookshop opens at the National Portrait Gallery. It's a handsome yet modest start to a major re-building programme which aims to get together all the Tudor paintings dispersed around the Portrait gallery. They are also adding a contemporary gallery and a new foyer, sliding an extension into a narrow slot in a courtyard shared between the National Gallery and the National Portrait Gallery.
Once again, Dixon and Jones have shown their skillful manipulation of the spaces in between existing buildings. Sympathetic to history, they are making a palimpsest of historic London which harks back to Inigo Jones, Nash and Wren, overlaid with a purposeful architecture that doesn't ignore the needs of its inhabitants for the 21st century.