The firm – which is led by former Foster + Partners partner Ken Shuttleworth – stripped back the interior to reveal its original features, then restored the metalwork and glasswork, as well as the windows.
The architects removed landings between the first and fifth floors, creating a central void that allow views between levels. Eight new pairs of escalators were added on opposite sides of this new atrium, allowing customers to easily move between different retail areas.
The nickel bronze that wraps the curvilinear underside of the elevators is marked with lines – a tribute to the original 1930s detailing.
"Layers of post- 1930s refurbishments have been stripped away to reveal the original features, and new contemporary interpretations of the materials and finishes have been applied to complement the art-deco design, concentrating on the themes of permanence, longevity and elegance," said the architects.
"The 16 new escalators themselves have been designed to be sculptural rather than purely functional, with bespoke ribbed and fluted nickel-bronze cladding used to define the fluidity and emphasise the movement," they said.
A new domed glass roof tops the circulation well to bring plenty of light into the hall, and 1930s chandeliers offer illumination.
The walkways that link the escalator hall with the retail areas feature grey stone walls and floors.
The architects also made a clearer entrance point for shoppers entering from the street, by adding an enlarged, solid canopy and revising the seating area outside the building.
Photography is by the architects, apart from where otherwise indicated.