Handel was the code-name for the United Kingdom's national attack warning system in the Cold War that was in place between 1962 and 1992. It consisted of two injection sites (RAF High Wycombe and the Royal Observer Corps Group 21 bunker in Goosnargh, Lancashire) linked to a series of two hundred and fifty-two carrier control points installed in major police stations; in turn, the control points were linked to several thousand receiver units installed at "warning points" in various police, fire, and coastguard stations, government buildings, hospitals, industrial centres, and Royal Observer Corps posts, with sufficiently remote areas having the units installed in post offices, public houses, churches, or even private dwellings.
A Handel warning console can be seen at the Imperial War Museum in London among their Cold War exhibits, alongside the warning apparatus used by Kent Police (which was located at Maidstone police station to activate the sirens).
If an enemy attack was detected, a key on the left-hand side of an "operating unit" console at one or both of the injection sites would be turned and two lights would come on; the operator would then press and hold down a red button and announce "Attack Warning Red". At the carrier control points, if one or both red lights flashed with a constant alarm, or if a white light flashed with an intermittent alarm, the control point operator was to lift the two red handsets (red lights) or the black handset (white light), listen for the injection site's "Attack Warning Red", and acknowledge it; they would then pass on their own "Attack Warning Red" to the warning points before activating powered sirens linked to the control point (some 7,000 sirens in total were linked to the system). Those manning the warning points would operate hand-cranked sirens (or activate any powered sirens they might have possessed) once they had received the attack warning message. The sirens would coincide with the broadcast of a "four-minute warning" on media channels.
Linked into Handel were the twenty-five Royal Observer Corps group controls, also with direct links to the carrier control points. As fallout from an eventual nuclear attack began to descend, "black" fallout warnings could be generated from the group controls on a localized basis over the same carrier wave system. Handel was also intended for use in communicating the eventual "white" all-clear message.
Initial Handel equipment fell under the WB400 and WB600 series of designations; this was upgraded from 1982 onwards to an EMP-resistant equipment line falling under the WB1400 series of designations. WB1400-series receivers were also trickle-charged to ensure that they would work when needed (while earlier receivers often suffered from unnecessary battery drainage due to being erroneously left on outside of test periods). The "operating unit" console at the injection sites was known as the WB1800.
The Handel system was based around the telephone system used for the speaking clock. The rationale for piggybacking off the speaking clock system was to tackle two problems at once; it reduced running costs (Handel would most likely be used only once in its working life, though it was regularly tested) and the telephone lines were continually tested for readiness by sharing infrastructure with a public service, meaning a fault could be detected and repaired in time to give a warning.