The Parliament of Great Britain was formed in 1707 following the ratification of the Treaty of Union by Acts of Union passed by the Parliament of England (established 1215) and the Parliament of Scotland (c.1235), both Acts of Union stating, "That the United Kingdom of Great Britain be represented by one and the same Parliament to be styled The Parliament of Great Britain." At the start of the 19th century, Parliament was further enlarged by Acts of Union ratified by the Parliament of Great Britain and the Parliament of Ireland, which abolished the latter and added 100 Irish MPs and 32 Lords to the former to create the Parliament of the United Kingdom of Great Britain and Ireland. The Royal and Parliamentary Titles Act 1927 formally amended the name to the "Parliament of the United Kingdom of Great Britain and Northern Ireland",[1] five years after the secession of the Irish Free State.

 

Print of the Palace of Westminster, before it burnt down in 1834

The United Kingdom of Great Britain and Ireland was created on 1 January 1801, by the merger of the Kingdoms of Great Britain and Ireland under the Acts of Union 1800. The principle of ministerial responsibility to the lower house (Commons) did not develop until the 19th century—the House of Lords was superior to the House of Commons both in theory and in practice. Members of the House of Commons (MPs) were elected in an antiquated electoral system, under which constituencies of vastly different sizes existed. Thus, the borough of Old Sarum, with seven voters, could elect two members, as could the borough of Dunwich, which had almost completely disappeared into the sea due to land erosion.

Many small constituencies, known as pocket or rotten boroughs, were controlled by members of the House of Lords, who could ensure the election of their relatives or supporters. During the reforms of the 19th century, beginning with the Reform Act 1832, the electoral system for the House of Commons was progressively regularised. No longer dependent on the Lords for their seats, MPs grew more assertive.

The supremacy of the British House of Commons was reaffirmed in the early 20th century. In 1909, the Commons passed the so-called "People's Budget," which made numerous changes to the taxation system which were detrimental to wealthy landowners. The House of Lords, which consisted mostly of powerful landowners, rejected the Budget. On the basis of the Budget's popularity and the Lords' consequent unpopularity, the Liberal Party narrowly won two general elections in 1910.

Using the result as a mandate, the Liberal Prime Minister, H. H. Asquith, introduced the Parliament Bill, which sought to restrict the powers of the House of Lords. (He did not reintroduce the land tax provision of the People's Budget.) When the Lords refused to pass the bill, Asquith countered with a promise extracted from the King in secret before the second general election of 1910 and requested the creation of several hundred Liberal peers, so as to erase the Conservative majority in the House of Lords. In the face of such a threat, the House of Lords narrowly passed the bill.

The Parliament Act 1911, as it became, prevented the Lords from blocking a money bill (a bill dealing with taxation), and allowed them to delay any other bill for a maximum of three sessions (reduced to two sessions in 1949), after which it could become law over their objections. However, regardless of the Parliament Acts of 1911 and 1949, the House of Lords has always retained the unrestricted power to veto any bill outright which attempts to extend the life of a parliament.[2]

The result of the 1918 general election in Ireland showed a landslide victory for the Irish republican party Sinn Féin, who vowed in their manifesto to establish an independent Irish Republic. Accordingly, Sinn Féin MPs, though ostensibly elected to sit in the House of Commons, refused to take their seats in Westminster, and instead assembled in 1919 to proclaim Irish independence and form a revolutionary unicameral parliament for the independent Irish Republic, called Dáil Éireann.

In 1920, in parallel to the Dáil, the Government of Ireland Act 1920 created home rule parliaments of Northern Ireland and Southern Ireland and reduced the representation of both parts at Westminster. The number of Northern Ireland seats was increased again after the introduction of direct rule in 1973.

The Irish republicans responded by declaring the elections to these home rule Parliaments, held on the same day in 1921, to be the basis of membership for a new Dáil Éireann. While the elections in Northern Ireland were both contested and won by Unionist parties, in Southern Ireland, all 128 candidates for the Southern Irish seats were returned unopposed. Of these, 124 were won by Sinn Féin and four by independent Unionists representing Dublin University (Trinity College).[3] Since only four MPs sat in the home rule Southern Irish parliament, with the remaining 124 being in the Republic's Second Dáil, the home rule parliament was adjourned sine die without ever having operated.

In 1922, pursuant to the Anglo-Irish Treaty, the revolutionary Irish Republic was replaced by the Irish Free State, recognised by Westminster as independent, while Northern Ireland would remain British, and in 1927 parliament was renamed the Parliament of the United Kingdom of Great Britain and Northern Ireland.

Further reforms to the House of Lords were made in the 20th century. The Life Peerages Act 1958 authorised the regular creation of life peerage dignities. By the 1960s, the regular creation of hereditary peerage dignities had ceased; thereafter, almost all new peers were life peers only.

The House of Lords Act 1999 removed the automatic right of hereditary peers to sit in the House of Lords, although it made an exception for 92 of them to be elected to life-terms by the other hereditary peers, with by-elections upon their death. The House of Lords is now a chamber that is subordinate to the House of Commons. Additionally, the Constitutional Reform Act 2005 led to abolition of the judicial functions of the House of Lords with the creation of the new Supreme Court of the United Kingdom in October 2009.