It is the second major office revamp job to be awarded by Derwent London to bam after it successfully overhauled a former Bank of Scotland office building in the Angel.
Bam will alter and extend 1 Page Street in Westminster, which was used by Westminster Hospital in the 1960s and more recently as a home for the Department for Environment, Food and Rural Affairs.
The 110,000 sq ft scheme will include a steel frame extension, removal and disposal of the existing façade and replacing it with modern brick and punched windows.
New lifts, external works, and mechanical and electrical services will be provided, as well as raised floors and suspended ceilings.
Construction director Mike Donegan said: “The project will require a comprehensive reworking of the existing building, particularly given its historic uses.
“The London commercial sector is beginning to improve after a difficult few years and BAM is proving that it is well placed to play a big role in its future.”