<P> Walpole always denied that he was "prime minister", and throughout the 18th century parliamentarians and legal scholars continued to deny that any such position was known to the Constitution . George II and George III made strenuous efforts to reclaim the personal power of the monarch, but the increasing complexity and expense of government meant that a minister who could command the loyalty of the Commons was increasingly necessary . The long tenure of the wartime prime minister William Pitt the Younger (1783--1801), combined with the mental illness of George III, consolidated the power of the post . The title was first referred to on government documents during the administration of Benjamin Disraeli but did not appear in the formal British Order of precedence until 1905 . </P> <P> The prestige of British institutions in the 19th century and the growth of the British Empire saw the British model of cabinet government, headed by a prime minister, widely copied, both in other European countries and in British colonial territories as they developed self - government . In some places alternative titles such as "premier", "chief minister", "first minister of state", "president of the council" or "chancellor" were adopted, but the essentials of the office were the same . </P> <P> By the late 20th century, the majority of the world's countries had a prime minister or equivalent minister, holding office under either a constitutional monarchy or a ceremonial president . The main exceptions to this system have been the United States and the presidential republics in Latin America modelled on the U.S. system, in which the president directly exercises executive authority . </P> <P> Bahrain's prime minister, Sheikh Khalifah bin Sulman Al Khalifah has been in the post since 1970, making him the longest serving non-elected prime minister . </P>

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