For your eyes only: MI5 shares unseen images of its former Mayfair HQ, where 'Registry Queens' carried out phone-tapping

It was founded 112 years ago amid escalating tensions with Imperial Germany.

Since then, MI5's spies have worked in the shadows to snoop on targets, foil bomb plots and keep leading politicians informed.

But now, the domestic intelligence agency, which is also known as the Security Service, has said goodbye to secrecy and revealed the inside of its former Mayfair base for the first time.  

Posting the 'for your eyes only' pictures on it's Instagram account, the spy agency said: 'More than 25 years after MI5 left the building for the last time, we're now pleased to be able to share some rare images of our Curzon Street office, the home of MI5 between 1977-1994.'

The collection of five photos shows female intelligence officers at their desks at 1-4 Curzon Street, known as 'Curzon Street House', where the Security Service housed its registry, administration and technical services departments.

The female staff were known as 'Registry Queens' and it was here that phone-tapping and other electronic surveillance methods were monitored.

MI5 has taken to instagram to share images of its former headquarters in Curzon Street, Mayfair. Above: A female member of staff sits at a machine in the undated photo

The collection of five photos shows female intelligence officers at their desks at 1-4 Curzon Street, known as 'Curzon Street House', where the Security Service housed its registry, administration and technical services departments. MI5 vacated the building in 1994

In one photo, a dark-haired spy is seen listening back to a reel of tape, presumably of a covert surveillance.

Another photo shows an office with women apparently listening to recordings.

A third shows a female officer changing a spool of tape on a machine.

Built in the 1930s, the most noticeable feature of the building was the absence of windows on the street level.

Higher floors were hidden by weighted net curtains to prevent prying eyes.

In one photo, a dark-haired spy is seen listening back to a reel of tape, presumably of a covert surveillance

Another photo shows an office with women apparently listening to recordings 

A third image shows a female officer changing a spool of tape on what appears to be a recording device

Writing on Instagram, MI5 added: 'Although there was never any official mention of MI5's offices at Curzon Street, bus conductors and taxi drivers were far less discreet.

'One former colleague recalls, "When you got off the bus in Park Lane the conductor would shout down the bus 'Curzon Street and MI5' and all of us would troop off looking somewhat embarrassed!"'. 

Prior to moving to 'Curzon Street House', MI5 housed its registry department on the ground floor of the street's Leconfield House. 

Also seen in the collection is an image showing a series of machines on wheels. Writing on Instagram, MI5 added: 'Although there was never any official mention of MI5's offices at Curzon Street, bus conductors and taxi drivers were far less discreet. One former colleague recalls, "When you got off the bus in Park Lane the conductor would shout down the bus 'Curzon Street and MI5' and all of us would troop off looking somewhat embarrassed!"'

It was there that in famous MI5 whistleblower Peter Wright was based before he wrote his explosive book Spy Catcher following his retirement. 

He revealed how the service 'bugged its way across London' and also alleged that MI5 boss Sir Roger Hollis was a Russian spy. 

The book was published first in Australia but was initially banned in England due to Wright's explosive allegations.

Prior to moving to 'Curzon Street House', MI5 housed its registry department on the ground floor of the street's Leconfield House

However, the book was still available elsewhere and the attempted censorship only increased its popularity. 

In mid-1987, a previous ban on English newspapers reporting about the book was lifted. 

A year later, the book was cleared for sale and sold more than two million copies, making Wright a millionaire when he died in 1995. 

Since 1994, MI5 has been based at Thames House, a building it had previously occupied in the 1930s. 

It's post on Thursday came after the service joined Instagram in April. In its first post, it shared a picture from the lobby of its Thames House headquarters. 

It said @mi5official will 'bust popular myths about its work, provide explainers for intelligence terminology, promote career opportunities and bring to life events in MI5's 112-year past'. 

Earlier this year, MI5's director general Mr McCallum said he wanted the traditionally highly secretive agency to 'open up and reach out in new ways'.

'Much of what we do needs to remain invisible, but what we are doesn't have to be,' he said in his first media engagement in October, after taking up the job in late April.

'In fact, opening up is key to our future success,' added McCallum, a MI5 veteran of more than 25 years who oversaw all counter-terror operations around the 2012 London Olympics.

The first ever post by MI5 on Instagram shows a frame of the entrance, where workers step int security pods before entering the building

Those behind the Instagram account for MI5 joked that the floor-to-ceiling angle of the shot could give aspiring spies a 'better view'