The UK Government Communications Headquarters (GCHQ), exposed for its mass surveillance programme by ex-NSA agent Edward Snowden, has for 66 years operated right in the heart of Westminster.

"For the first time, we are able to reveal the role our Palmer Street office has played in keeping the capital and the country safe," said GCHQ in a statement, speaking about an anonymous building opposite St. James's Park Tube station in central London.

The spy agency has now left the building and is eyeing a new secure facility in Manchester as part of its network extension project.

"As we depart our Palmer Street site after 66 years, we look back on a history full of amazing intelligence, world-leading innovation, and the ingenious people who passed through those secret doors. Then, as now, it's a history defined by the belief that with the right mix of minds, anything is possible," Director of GCHQ, Jeremy Fleming said.

GCHQ's headquarters are located in Cheltenham, while its other offices are based in Bude in Cornwall, Scarborough, Lincolnshire and Harrogate. The agency's National Cyber Security Centre was opened in 2017 near Victoria in London.

— The Royal Family (@RoyalFamily) February 14, 2017​

Throughout its 100 years of operation, GCHQ has most recently come into the limelight, after it was revealed it was running an operation called "Tempora" that allowed it to tap into and store large volumes of data, including phone calls, messages and internet communication.

READ MORE: UK Expansive Overseas Surveillance Bill Puts Journalists at Risk — Watchdogs