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Who is the Architects' Architect of the moment? Certainly, Lords Rogers and Foster are still spoken of in hushed tones by their peers. But if the best definition of the architects' architect is the one other architects would trust to design their own homes, then young London partnership Munkenbeck + Marshall scores high.

The evidence can be found in a loft conversion of 14 apartments designed by the practice for the Mod Group and lying just off Edgware Road in London's Marylebone. Occupants in an earlier phase completed two years ago include Graham Stirk and Carmel Lewin, senior architects at Richard Rogers Partnership, and Tom Croft, partner of Rick Mather. In the newly completed second phase, all but one of the nine flats have gone to design or media moguls, according to Mod director Richard Claydon.

Added to that, the largest apartment of all, a grand 300 m sq duplex penthouse, is being converted by Terry Farrell from half his practice's former offices above and beside the Mod scheme, and Farrell has opted to incorporate Munkenbeck + Marshall's kitchen design within his own conversion design.

There is nothing revolutionary in Munkenbeck + Marshall's loft designs. Rather, it is their distillation of spaces, materials and detailing in the clean-cut, no-frills modernist tradition that seems to appeal to other architects, particularly in the second phase.

Two years ago in an earlier phase of the conversion, the concrete structure was left as found, all gouged and stained, and raw-looking spiral staircases were added to match. But now this industrial radical-chic is beginning to look affected. With rocketing property prices and Porsches lining the street below, the myth of the poor bohemian loft dweller has become hard to sustain.

In the newly completed second phase, only the industrial building's best aspects – wide, lofty interiors and huge windows – have been retained, and have been fully refurbished and fitted-out with kitchen and bathrooms in a more consistently sophisticated manner. This sophistication reaches its zenith in the upper storey of the £725 000 penthouse duplex, which is a cool, cleanly detailed Miesian pavilion in steel and glass.

Named the Old Aeroworks, the building was constructed in the 1930s in a basic art deco design by Wallis, Gilbert & Partners, architect of the iconic Hoover and Firestone buildings along the Great West Road. Originally a tyre factory, its name derives from its use during the Second World War to manufacture components for Spitfires. And, since 1985, it has served as the offices of Terry Farrell & Partners, which added its own brightly coloured postmodern ornamentation. Farrell has now moved his offices next door while converting part of his original offices on the top floor into his own grand studio flat.

In Mod's phase two conversions, the industrial aesthetic has become more like that of an art gallery. All wall and ceiling surfaces, including the reinforced concrete frame, have been painted white. These plain white surfaces are enhanced by minimalist detailing such as recessed shadow-gap skirting lined in grey-painted steel angles and the complete lack of architraves, made possible by concealing thin steel door-frames within the plaster reveals.

The steel frames to the huge window openings have been replaced in updated Crittal W20 frames incorporating double-glazing panels. Floors are also true to form in natural timber boarding, in this case hefty planks of American oak.

Kitchens and bathrooms are models of refined luxury, although modest in scale. The kitchens are little more than plain oak-veneered cabinets and polished stainless steel worktops with integral sinks, a nice balance of natural and hygienic materials. The bathrooms feature polished marble floors and unglazed ceramic wall-linings midway in scale between between tiles and mosaic.

Any last vestiges of the building's industrial character have been abandoned in the new upper floor of the penthouse maisonette. The vast space is enclosed on three sides by sliding window walls that can retract fully for an unimpeded panorama of west London. Overhead, a wide barrel-vaulted roof of translucent fibre-glass imported from the USA adds to the unrestricted space and light.

There is more to the conversion than tacking on refined detailing and painting everything white. The lofts are graced by their sequences of well-lit and decently proportioned rectangular spaces. Yet these clearly defined spaces, which avoid any awkward changes of level, did not come ready-made; in fact, they required radical remodelling of the existing building.

"We took out the existing staircases, which were on a prime corner of the building with the best views," explains James Biek, associate of Munkenbeck + Marshall. "And we had to cut a new stair and lift core through all the concrete floors." Other structural interventions included replacing the metal roof of the corner tower with a concrete deck, to support the upper floor of the penthouse, and reordering window openings on the upper floors.

There is, however, one dampener on this scene of open-plan finery: as well as offering occupants splendid views, the huge windows give tenants of the neighbouring 1930s council flats an unrestricted view into the converted lofts and penthouse.

No doubt the relatively low prices for what Mod's Claydon calls "a little oasis in council estates" brings the converted lofts within the reach of architects. This just adds to the architect appeal of Munkenbeck + Marshall's distilled conversion designs.

Farrell's living space

Architect Terry Farrell is creating the grandest of the new loft apartments in the Old Aeroworks by converting half of the former offices of his practice.

The open volume of the top floor has been retained as a vast studio-cum-living space beneath the roof void and stretching from the front to the rear of the building. A central staircase from the floor below, flanked by large urns, has been retained to give the spectacular entrance that is Farrell's trademark.

"I wanted a very large open space," says Farrell. "All our children have left home, and we plan to use it as a studio and a place to entertain our friends."

The other rooms of the 300 m2 duplex have been restrained from encroaching on the vast studio space. Kitchen and bathroom have been placed into two corners along one party wall, and two compact bedrooms have been tucked directly above them below the double-pitched metal roofs. As the bedrooms are short on space, fitted cabinets line three walls.