Client Land Securities said construction can now go-ahead at Kingsgate House after legislation was changed this week to prevent a planning levy for local infrastructure being double-charged.
Lend Lease has been lined-up as main contractor after fighting off competition from Mace and Sir Robert McAlpine.
The announcement came as the Government introduced the Growth and Infrastructure Bill to Parliament.
Ministers claim the package will unlock billions of pounds worth of investment by easing bureaucratic burdens on developers and employers.
Cameron said: “Already the changes we are making to the planning system are having an impact, with Land Securities giving the go-ahead to a major multimillion-pound investment, supporting thousands of jobs in our construction industry.”
Land Securities chief executive Robert Noel said: “It is heartening to know that Government has listened to the industry and acted to remove some of the uncertainty in the planning process.
“It enables us to take forward the development of the former Kingsgate House site and continue our transformation of Victoria to a distinct and vibrant West End hub.”