There is not only a risk of the deliberate use of nuclear weapons; they could also be detonated as a result of human error, technical malfunction, cyber-attack, misinterpreted warnings or unauthorised access to command and control systems.

The numerous accidents involving nuclear weapons since 1945, as well as incidents where they were almost used due to errors, demonstrate the alarming potential for unintended disaster.

In 1968, for example, a US aircraft carrying four nuclear bombs caught fire and crashed near Greenland, contaminating the surrounding area with plutonium. Luckily, though explosions did occur, no nuclear chain reaction was triggered.

In 1995, Russian officials mistook the launch of a Norwegian scientific rocket for a US submarine-launched ballistic missile. The Russian president retrieved the launch codes for a retaliatory strike but ultimately determined that it was a false alarm.

Other deeply troubling incidents have involved the loss of nuclear weapons at sea, nuclear-armed submarines colliding, flying swans and light reflected off clouds being mistaken for nuclear-tipped missiles, and the inadvertent insertion of training tapes into an operational computer, which simulated an incoming nuclear attack.