Southwark Council is the new owner of the Courage Yard complex of homes, shops and offices next to Tower Bridge.
Formerly known as Tower Bridge Piazza, the mixed-use 1980s development on Shad Thames includes shops, offices and flats.
The latest investment will generate around £5 million a year in revenue.
Cllr Victoria Mills, cabinet member for finance, performance and Brexit, said: "Income we receive from our commercial property portfolio is essential to help support our highly valued public services in this time of decreasing government funding.
"Over the years we have acquired commercial assets that we can manage to generate revenue. Projects are chosen based on being in Southwark and the size and resilience of their revenue return, which can then be used to support our frontline services.
"Over recent years a number of properties the council owns have been sold to help finance our substantial capital programme or we have developed them to deliver new council housing. This has reduced our income from commercial assets.
"During 2017 we purchased four properties in the borough with an established rental income of over £2.18 million a year and we believe that Courage Yard will be another valuable asset for the council."
To date the retail element of the development has never lived up to its potential, with units often remaining empty for years at a time.
In 1986 Courage Yard – then known as Horselydown Square – was described rather optimistically in adverts placed by developer Berkeley House as "the exciting new Covent Garden of the Docklands".
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