The BT Tower in Lionel Street stands 152 metres high, making it the tallest structure in Birmingham. It has been an icon of the city’s skyline for almost 50 years and can be seen from many miles away.

It was designed and constructed by the Ministry of Public Building and Works and was opened by the Lord Mayor of Birmingham in 1967. Some may remember its many names over the years, such as the General Post Office (GPO) Tower, Birmingham Radio Tower and Telecom Tower.

Before the introduction of the fibre network, telecom towers across the country formed the backbone of British communications. When it was built, the tower’s height was key to its success, avoiding surrounding buildings to allow direct line of sight of radio waves to London and other towers across the UK.

Despite its utilitarian architecture, the BT Tower has found its way into public affection. Its concrete shaft is reassuringly robust, with articulated corners, which help resist wind movement that could disrupt communications. In 2003 a striking new colour scheme was applied, helping to accentuate its recessed corner windows and deep window sills.

The distinctive circular concrete finial at the top, known as the aerial gallery, supports the remaining satellite dishes. Although the last of the large dishes was removed in 2012, it is still very much an operational tower. Around 80 smaller dishes remain, each about half a metre in diameter, providing high speed data to businesses and broadcast media in locations where the fibre network is not available.

Stepping through the secure doors at ground level is like stepping into another world, 25 floors each with their own unique function. Exploring these working floors involves weaving through a high-tech labyrinth of cables, blinking lights, state of the art radio equipment and network racks, known as Access Radio.

On one of the floors the redundant control room for the national trunk network is still in place, following its decommissioning around four years ago. The original telephone exchange equipment remains, including the iconic ’70s design Trimphones; relics of the telecom of yesteryear and a reminder of how far communication technology has advanced.

Other floors in the building remain operational as equipment maintenance and repair centres, while others house testing facilities and spare parts, or simply storage of archives. There is even a mess and dining floor for workers.

At the top of the tower is a vast three storey hollow concrete cube, which on the outside displays the giant BT logos. This space, known as the band branch room, contains little more than a web of massive cables and a long ladder, which ascends through a narrow opening to the aerial gallery.

The top of the tower offers a true bird’s eye view of the city centre and on a clear day you can see for miles around. In this lofty vantage point, several special residents have made their home. For several years now, a pair of peregrine falcons have nested on a ledge on the 22nd floor.

In consultation with the RSPB, the ledge has been specially modified by BT engineers to form a pebbled nesting tray that resembles their natural cliff-top habitat. This has paid dividends and this year, for the first time since the pair’s arrival, several chicks have hatched.