Council chiefs are pressing ahead with the headquarters overhaul as maintenance of the 1960s building has become increasingly difficult and costly.
The 19-floor tower revamp is expected to take up to two years to complete and is due to get underway early in 2017.
Designed by BDP, the 64 Victoria Street project will include repair and cleaning of the external stonework and the replacement of all windows.
Internally the contractor will replace building services and install new lifts. The 19th floor will be improved with floor to ceiling windows and new plant fitted to the roof, raisjng the building’s height slightly.
According to construction information specialist Glenigan ISG is bidding against Wates and Graham Construction for the big refurb job.
Faithful & Gould is acting as the cost consultant.
Councillor Robert Davis MBE DL, Deputy Leader and Cabinet Member for the Built Environment, said: “City Hall plays an important role in the public life of Westminster but it is currently underperforming, both for visitors and staff as well as environmentally.
“That’s why proposals have been brought forward to refurbish the building in the most efficient and effective manner that will deliver savings, future income and a ‘greener’ civic space for many years to come.”