The courts were established in response to a report by Lord Diplock, which addressed the problem of dealing with paramilitary violence through means other than internment. The report marked the beginnings of a policy known as criminalisation, in which the state removed any legal distinction between political violence and normal crime, with paramilitary prisoners treated as common criminals. This led to the hunger strikes of 1981.
The report provided the basis for the Northern Ireland (Emergency Provisions) Act 1973, which, although later amended (as the Prevention of Terrorism (Temporary Provisions) Act 1974 and subsequent renewals), continued as the basis for counter-terrorist legislation in the UK.
Until recently the Diplock courts only tried Republican or Loyalist paramilitaries. In the first case in which a person not associated with the Troubles was tried and convicted, Abbas Boutrab, a suspected al-Qaeda sympathizer, was found guilty of having information that could assist bombing an airliner. A sentence of six years was handed down on December 20, 2005.
The number of cases heard in Diplock courts reached a peak of 329 a year in the mid-1980s. With the Northern Ireland peace process that figure fell to 60 a year in the mid-2000s. On 1 August 2005, the Northern Ireland Office announced that the Diplock courts were to be phased out, and in August 2006 they announced that the courts were to be abolished from July 2007. Non-jury trials would still be used in Northern Ireland, but only in exceptional cases. In fact, the trial of Chris Ward, who has been charged with robbery and false imprisonment relating to the infamous Northern Bank Robbery in Belfast in 2004 in which £26.5m was stolen, will be held in a Diplock Court.