Guardian telephone exchange

Guardian Exchange was an underground telephone exchange built in Manchester in 1954. It was built together with the Anchor Exchange in Birmingham and the Kingsway exchange in London – all believed to provide hardened communications in the event of nuclear war. Today the underground site is used for telephone cabling. Constructed at a depth of 35 metres (115 ft), the tunnels are about 2 metres (80 in) in diameter. The exchange cost around £4 million (approximately £126 million in 2015 prices), part of which was funded by the United Kingdom's NATO partners.

Use as a nuclear bunker
The Guardian Bunker has been called the "Best kept secret in Manchester" and its existence was only publicly acknowledged in 1968, 14 years after initial construction.

Use as a telephone exchange
The tunnels are known to be used for British Telecom cables. The exchange rose to prominence in March 2004 when a fire in one of the tunnels caused 130,000 telephone lines in Manchester to be cut off. Ambulance and fire service calls around the North West region were also severely affected.