Fashion victor: Nestling beside London's Westway, a former motorway maintenance building has been stylishly recast as a fashion company headquarters.

Motorists barrelling along London's Westway, the iconic elevated motorway that snakes westward out of the metropolis, are probably familiar with the equally iconic Paddington Maintenance Depot, a Heroic Modernist confection of nautical curves and streamlining that docks within a hair's breadth of whizzing streams of cars. Designed in 1968 by Bicknell and Hamilton, it was a something of a showpiece, intended to complement the newly constructed Westway as a statement of engineering power and prowess. The muscular, interlocking volumes (a low tower straddling a three-storey office block) have a certain period drama when seen at speed from the motorway. Emphasizing the nautical analogy, the lowest floor extends into a curved prow.

The Paddington Maintenance Depot has had an intriguingly chequered career. When it outlived its original use as a maintenance and repair centre for the Westway, it fell into a state of languishing neglect. Demolition was seriously contemplated, but it was saved and listed Grade II (*) in the early 1990s, following campaigns by activists. Being such a site and function-specific building, however, there was little commercial or architectural enthusiasm for its recolonization and the brooding, derelict hulk became a familiar backdrop to illegal parties and gatherings.

Now it has been reincarnated, slightly improbably, as the headquarters of Monsoon, a British-based fashion company known for its distinctive, ethnically inspired clothing. The company wanted to bring its various management offices and design studios under one roof and were astute enough to recognize the potential of Bicknell and Hamilton's building, despite its recent history. The wider urban context is also changing: on the opposite (south) side of the Westway, the Paddington Basin development is currently transforming an industrial wasteland into a gargantuan complex of offices, shops and swanky apartments.

Allford Hall Monaghan Morris were commissioned to revive, remodel and recast the building. With projects such as the new Walsall bus station (AR June 2000) and housing for the Peabody Trust in Dalston (AR November 1999), AHMM are acquiring a reputation for diligent and inventive architecture that has its ideological roots in British Modernism. This most recent scheme consolidates and refines their thoughtful approach.

Externally, the building has simply been tactfully tidied up. The glistening veneer of cream mosaic tiles (originally from Japan) has been restored and the concrete frame cleaned. The strong, visor-like bands of glazing are also retained, but replaced with double-glazed units and a secondary line of glazing to improve acoustic conditions. The effect is miraculous; even in the offices and design studios overlooking the motorway, you can hear a pin drop, while cars glide soundlessly past, like supercharged fish in a giant aquarium. Internally, former cellular spaces have been opened up to great effect. A spinal core of circulation and ancillary spaces runs lengthways across the floorplates, serving open-plan wings of offices, studios and showrooms on each side. The spine is terminated by the building's original main staircase, contained in a toplit well lined with pale turquoise mosaic tiles, a curiously delicate moment amid the robust Modernism.

The original spaces have proved surprisingly adaptable. Even the plant rooms on the lower levels have been transformed into double-height office spaces with mezzanine galleries running along the inner edge. Here the physical presence of the motorway is unavoidable as its superstructure looms over the building, but sail-like uplighters bounce and diffuse light up through the tall volume. The other main move is a new triple-height void gouged through the centre of the spine. This unifies spaces on the lower floors, creating through views, and revealing glimpses of the working environment to visitors. Naturally, the topmost floor is reserved for the upper echelons of management, with the grandest office and its roof terrace resembling the bridge on a ship.

The neighbouring Rotunda Building (the former vehicle depot) has also been refurbished to provide separate lettable office space. The refurbished zinc roof forms an arresting contrast with the cream tiled and rendered walls of the main building. Pedestrian access and routes have also been improved; this was an important consideration, given the site's impermeability (enmeshed by motorways and slip roads) and that many staff will arrive on foot. New bridges over the Regent's Canal will link the building with the emerging swathes of Paddington Basin to the south and Little Venice to the north. From splendid destitute isolation to a new use and reconnection with the urban realm, this '60s icon has been skilfully and stylishly reborn. C.S.