The head of Parliament was the reigning monarch, even though it was actually led by the Prime Minister, who attained their position via their ability to command a majority vote in Parliament and an official appointment from the monarch. The Prime Minister then formed a Government by recommending members of Parliament to serve as Ministers of various executive departments, such as the Foreign Ministry.
Parliament was a bicameral congress, consisting of an upper house, the House of Lords, and a lower house, the House of Commons. Both houses had the power of self-veto, so one was able to cancel resolutions of the other. The Prime Minister was constitutionally required to be a member of the House of Lords. The King or Queen – whose office was orderly marked as the Crown – also had the power of veto and could introduce legislation. (HH2)
The influence of the Crown in Parliament was such that the monarch usually was able to influence who could hold enough power to be Prime Minister, and to a lesser extent the political positions of the Government. However, governments which operated without the approval of the Crown, or without support in the House of Commons, or both, were possible, the most infamous example of which was the High Ridge Government of the 1910's PD. (HH10)
In 1903 PD, the Cromarty government, led by Prime Minister Allen Summervale, was in control of a majority in Parliament that consisted of a coalition between Cromarty's Centrist Party, the Crown Loyalist Party, the Conservative Association (until approximately 1905 PD), and several independent peers. Cromarty had been in power for decades with the full confidence of Queen Elizabeth III. (HH2, HH4)
In 1915 PD, Duke Cromarty was assassinated by Masadan extremists during Operation Hassan, in the service of the People's Republic of Haven. With his death went the personal alliances between him and several independent members of the House of Lords necessary to maintain his slim working majority, allowing the leaders of the Opposition to form a new government under Baron High Ridge to the exclusion of Cromarty's centrists (HH9)
In 1920 PD, after the Havenite suprise attack (Operation Thunderbolt) that constituted the worst military defeat in the Star Kingdom's history, High Ridge was forced to resign. The collapse of his government severely destabalized the Conservative, Liberal, and Progressive parties which had governed in coalition under him, allowing William Alexander to form a restored Centrist and Crown Loyalist-controlled regime.
Alexander was created Baron Grantville, and he became head of the new Grantville Government. (HH10)