The freehold of Southwark Council's Tooley Street headquarters has been put up for sale with a £150 million price tag.
Owned by private clients of HSBC Private Bank, the South Bank building is currently let to the authority on a 25-year lease that began in 2008, website CoStar reported.
Sitematch London sources at Southwark Council confirmed the story.
Agent Whitmarsh Holt Young had been instructed to sell the 205,236sq ft office building.
"We've already surpassed one degree of global warming," said Kristen Buida, manager of the London Climate Change Partnership.