GCHQ's top secret London base unmasked after coordinates kept hidden from public for over 65 years

GCHQ's former offices in Palmer street, Westminster. The location of what was the spy agency's base can only be revealed now that it has moved elsewhere (Picture: PA)

The location of spy agency GCHQ’s London base has been revealed after being unknown to the public for more than 65 years.

The whereabouts of the site, sandwiched between a Starbucks and a pub near St James’s Park Tube station, was until now top secret.

GCHQ, known as Britain's listening post, has successfully worked to protect the coordinates of the base since 1953. But the location of the site, in Palmer Street, has now been unmasked after the organisation moved elsewhere.

Director of GCHQ Jeremy Fleming said: "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.

The former base was top secret for many years (PA)

"Then, as now, it's a history defined by the belief that with the right mix of minds, anything is possible."

GCHQ was established on November 1 1919 as a peacetime "cryptanalytic" unit made up from staff from the Admiralty's Room 40 and the War Office's MI1(b).

During the Second World War, GCHQ personnel moved to Bletchley Park where they decrypted German messages, most famously by breaking Enigma communications.

In the early 1950s, the service moved its headquarters from the London suburbs of Eastcote to Cheltenham, meaning a suitable location was needed in the centre of the capital for the handling of secret paperwork and as a regular base for its director.

GCHQ has revealed its former offices were behind this door in Palmer street, Westminster (PA)

After a search, the Ministry of Works provided a newly built, Government-leased building on Palmer Street.

GCHQ moved into its secret London home in the spring of 1953, housing a range of different teams there over the following decades.

The agency said: "The Palmer Street hub has played its part in significant events over the years, such as the 2012 London Olympics, working with our partners, MI6, MI5 and the Metropolitan Police to counter terrorist activities and serious and organised crime whilst keeping ministers up to date with security briefings."

The future plans for the building, which has been sold privately, are not known.

While no longer operating from the Palmer Street site, GCHQ will maintain a London presence.

As well as its Cheltenham HQ, the agency has offices in Bude in Cornwall, Scarborough, Lincolnshire and Harrogate. Later this year, it will open a new secure facility in Manchester.

GCHQ works alongside MI5, MI6 and law enforcement to protect the UK from threats including cyber attacks and terrorism.