Mussel bound.

Belgo Centraal, a huge new restaurant in Covent Garden in the heart of London's theatreland, provides a subterranean spectacle of its own.

The nineteenth-century warehouses around Earlham and Shelton Streets in Covent Garden, built in the style of the London docks, form solid phalanx-like cliffs only broken by the old patterns of doorways and windows. Here and there an overhead hoist and pulley remind you that these were built as repositories for industries far removed from the design and dance studios, jazz clubs and community offices that now inhabit them.

The change of use, reminiscent of soft-shelled crabs moving into abandoned mollusc shells, is familiar. Inside, the brick wall/cast-iron column and beam construction typically yields a series of deep plan, low-ceilinged spaces stacked one upon the other and contained at the subterranean level beneath vaults. These buildings are fairly inflexible at every level: apart from adding or subtracting internal divisions you pretty well have to live with the structure. Nor is it easy to create, should you want to, a conventional shop window within those thick impassive walls.

In designing an enormous subterranean restaurant opposite the Donmar Warehouse theatre in Earlham Street, Ron Arad and Alison Brooks have summoned up their theatrical talents to deal with what in less imaginative hands could prove a commercial drawback. Within a dark amorphous cavern, the architects have conjured a spectacle that reveals itself bit by diverting bit from the moment you enter. Stepping onto the illuminated plates of a metal bridge at the entrance, you can peer down into the lighted restaurant, onto the heads of diners and gleaming kitchen, before being carried down in the silvered cage of a Gibbs goods lift. The spirit resident in the building is subterranean and industrial, and in their design, the architects have played games with it.

Belgo Centraal, like the original Belgo in Chalk Farm Road (where Ron Arad Associates designed an extension: AR November 1994), has waiters dressed as monks serving Belgian beer and food (mussels and chips) at affordable prices. With nearly 400 seats, its style is friendly and informal - not to say hugger-mugger at the refectory end. The kitchen is open and the cooking visible, which must impose its own strains, but as stars in the spectacle, the staff look cheerful enough.

The plan is wedge-shaped, running west from the apex of Earlham and Shelton Streets. (That part nearest the apex was once occupied by Smith's Restaurant which seems to have suffered terminal subterranean sickness.) The architects' stroke of inspiration was to have established entry from either street at around the middle of the wedge so that immediately there is some sort of shape. Such physical connection with the outside world is reinforced by a visual one. For the bridge that runs between the two streets was made by cutting away vaults and part of the mezzanine above on either side, so that there are not only views down into the restaurant from above, but up through the height of the cut to relieve subterranean oppression. As well as being underground, the open kitchen generates a lot of heat. The restaurant is therefore highly serviced, with ducting hidden below, but exposed above to form part of the paraphernalia surrounding entry.

Passengers disgorging from the lift are faced with the sight of the bustling kitchen and the oddly dressed waiters. On either side, the old brick vaults spread away, arching over cast-iron columns covered with silvery intumescent paint that makes them look curiously like stage props. To the right is the open communal area contracting at the far end into two vaulted cells used as private dining rooms, to the left is a more intimate area with strange glimmering partitions set around small tables and inset with shooting lights. Behind a partition of galvanised steel are lavatories: coloured cubicles behind concertinaed walls of prefabricated metal sheet and a communal fountain.

Arad is adept at hijacking the ordinary object and twisting perception of it while leaving function intact. At Belgo Centraal, the mechanism of a mundane goods lift has been made the focus of invention. It is raised and lowered on double (rather than the usual single) scissors whose illuminated silhouette, extending and folding, behind clouded glass panels casts magical shadows. More prosaically, the lift accepts wheelchairs. The deadly restaurant partition has been reinvented, made out of maple laminate (to form the curving backs of refectory seating) or of panels of galvanised steel folded like paper around lights or cloudy glass. Elsewhere over a bar counter, illuminated holes punched in the lowered ceiling simulate daylight and suggest open space above, and industrial steel mesh screens rows of beer barrels. The pleasure in stretching material limits and in reworking familiar forms and objects continually propels the work of this practice into the realms of art.

The only problem is that when crowded this restaurant is noisy, as sound reverberates off hard surfaces - but habitual clubbers addicted to cacophony are unlikely to notice.