1885年的大英國會有三個主要政黨：執政黨自由黨、在野黨保守黨、以及執政黨的友黨愛爾蘭黨。然而愛爾蘭黨一心想爭取自治而不可得，其政黨（兼民族）領袖巴奈爾乃統率起60席以上的愛爾蘭籍議員，在一項議案上與保守黨合作投反對票，造成自由黨政府6月的下台。保守黨因此得到翻身的機會，願考慮支持巴奈爾的自治條件以尋求雙方在國會議題上的合作；這激起了自由黨領袖格蘭斯頓的危機感，使他決定答應巴奈爾所提的自治法案，以拉攏愛爾蘭黨的支持。12月改選後，愛爾蘭黨的席次增加到86席，自由黨失去過半的優勢席次，讓愛爾蘭黨席次成為可左右國會的第三勢力。本文的目的在於闡明這段由愛爾蘭黨扮演的關鍵少數，對國會內兩大黨結構的撼動，進而造成國會生態改變，並奠下日後改革基礎的過程。文中首先說明愛爾蘭黨與保守黨合作的用意在督促格蘭斯頓採取進一步的政治措施，方使自治法案得以催生。其次說明格蘭斯頓推動自治法案的個人動機，既來自他對愛爾蘭議題的熱忱，更來自重新團結自由黨的渴望。再者說明自治法案遭致的質疑多而難解，使此法案不但難獲認同，更激起攸關聯合王國存續的厄斯特問題。接著說明5月後的政治新局，呈現出激進主義與保守主義各自拉攏結盟的態勢，國會權威在意識型態的對抗下得到進一步強化，最後由保守黨獲得過半勝選。自治法案雖被否決，國會結構與生態的自由主義化卻大為促進，此為愛爾蘭黨在1886年的根本影響。

In 1885 there were three main parties in British Parliament: Liberal Party (the ruling party), Conservative Party, and Irish Party. The Irish Party desired Home Rule and to achieve this goal Charles S. Parnell, the leader of Irish National Movement, united over 60 Irish MPs with the Conservative Party to vote against the Liberal Party's bill. This turn caused Gladstone's government to fall out of power in June 1885. In the interest of future cooperation, the Conservative Party was willing to concede to Parnell's request for Home Rule. The result was that Gladstone extended more benefits, particularly the Home Rule Bill for Ireland, to keep the support of the Irish Party. In December 1885, the general election showed a decrease in the Liberal Party's seats and an increase in the Irish Party’s seats (to 86), allowing the Irish Party to more strongly influence government policy. The goal of this article is to explain how Irish Party influenced the other two main political parties by using their ”key seats in small number” to get the Home Rule Bill, as well as broadly alter the circumstance of parliament in order to make reform easier.The first section examines the cooperation between the Irish Party and Conservative Party as a means to push Gladstone to take measures on the Home Rule Bill; the second section considers Gladstone's personal interest in Home Rule, especially his effort to unite the Liberal Party using single-question politics; the third section discusses why Home Rule had difficulty winning opposition approval; the fourth section explore the conflict between radicalism and conservatism in relation to this bill; and the final section sums up and interprets the historical position of the Irish Party in 1886.