Osborne was awarded the £40m construction contract in April but a site start was delayed while the developer looked for a pre-let tenant.
But Native Land has now decided to start work on a speculative basis and groundworks have begun on the OneThreeSix scheme on the former site of Regent House.
The scheme will provide six floors of Grade A office space alongside 25 premium apartments and retail units at street level.
Sophia Jarvie, Development Director at Native Land, said: “We are very excited to start the development of OneThreeSix, Native Land’s first major commercial development.
“With a track record of creating exceptional residential developments, we are now bringing that experience to bear on developing sophisticated workspaces with a new level of quality and service, reflecting the needs of a new generation of occupiers.
“The market is undersupplied and OneThreeSix will provide occupiers with a sustainable workspace of the highest quality, aimed at fostering wellbeing and productivity, in an exceptional central London location.”
Completion is scheduled for Q4 2020.