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New Street Station has been at the centre of public attention in recent times, with its extensive redevelopment works in full swing . However, at the heart of it, and often overlooked, sits the Grade II listed signal box on Navigation Street, which houses the centre of all rail operations of the station.

The corrugated concrete Brutalist structure may polarise public opinion, but is actually home of one of the city's most vital and intense infrastructure systems, serving the busiest rail interchange in the UK.

Designed by Bicknell & Hamilton and W.R. Healey and completed in 1965, the unapologetically bunker-like structure is an honest expression of its utilitarian function. Standing five storeys high above track level, the building gives no clue of the hive of activity that exists within its four walls.

The technology inside is of the same era as the exterior façade and was revolutionary for its time. The Relay Room sits just above street level and houses enormous banks of algorithmic electronic relays, known as Wespacs, which are programmed to calculate legal routes for the trains to take.

To maintain these systems, Network Rail engineers have to retain specialist knowledge of technology that is decades old. The long aisles of Wespacs are lit by incessantly flashing green and red lights and the extraordinary sound of thousands of relays clicking fills the room.

The top floor, or the Operational Floor, is reminiscent of the lair of a 1960s Bond villain. From their elevated perch a dedicated team operates 24/7, 365 days a year, and has done since the Signal Box opened.

Stood in front of a gigantic processing unit, which maps out the rail network with intertwining lines of LED lights and buttons, the team plan the routes for every train between Birmingham International and Wolverhampton.

Love it or hate it, signal boxes are soon to be a thing of the past. Over the next decade the signal boxes of the UK will be consolidated into centralised control centres where a single computer will control vast areas of track, a far cry from the ticking behemoths of the New Street Signal Box.

Thankfully, due its listed status, the humble concrete box on Navigation Street will remain a bastion for the romance of the railways, if only in spirit.

Matthew Goer, Associated Architects

The first Hidden Spaces feature looks at the opulence of Birmingham's Victorian Council House and its wartime secrets

We also take a look at the Chamberlain Clock Tower, also known as Big Brum and its commanding views across the city

Birmingham's mysterious Perrott's Folly is another of the buildings featured in the Hidden Spaces features

The full Hidden Spaces supplements are included in the Boxing Day and January 2 editions of the Birmingham Post