英國國會議員選舉長久以來採行單一選區相對多數決制，這 種選舉制度固然有助於形成政治責任清楚的單一政黨政府，但這 種選舉制度最受詬病之處，在於此制會產生嚴重的「比例性偏差」（ disproportionality）問題，使英國各政黨在選舉中所獲得的選票，無法在國會的席次中真實地反映出來。 2010年國會大選後，英國終於出現國會選制改革的契機，選後由保守黨與自由民主黨共同組成的聯合政府，提出了選擇投票制（alternative vote）的國會選制改革方案，並於 2011年 5月就是否改變國會選舉制度舉行公民投票。但是，最終公投結果仍未通過選制改革方案。 本文的目的在於檢視英國國會選制改革契機曙光乍現而終 致功虧一簣的過程。本文介紹了英國選制改革方案—選擇投票制 的內涵與可能效應，分析了英國政府提交公投的選制改革方案為 何是選擇投票制而非其他方案的緣由，並詳述了英國國會選制改 革公投最終無法成功的原因。從英國此次國會選制改革失敗的經 驗可以發現：受到現行選舉制度制約的政黨體系，仍有可能在現 行選舉制度下找到突破的空間，而跳脫選舉制度長期以來的束 縛，反過來去改變既有的選舉制度。以英國為例，英國的兩黨制 長期受到單一選區相對多數決制的塑造與制約，使得小黨生存空 間有限。然而，在 2010年國會選舉中，在單一選區相對多數決 制下仍例外地出現了各黨不過半的格局，使得自由民主黨在現行 選制下找到突破點，有機會促成選舉制度的改變，只是最終未能 成功。儘管英國此次選制改革最後以失敗收場，但從長期趨勢看 來，隨著小黨得票率與席次率的增加，英國目前的兩黨制正處於 不穩定的階段，將來國會大選仍有可能出現各黨不過半的格局。 在此格局下，國會選制改革的運動未來仍有機會捲土重來。

The UK parliamentary election system adopted the first-past-the-post system (FPTP) a long time ago. This electoral system helps build up a single-party government with clear political responsibilities, but it also creates a serious “disproportionality＂ problem where the parliamentary seats each party gets are not proportional to the votes it receives. After the parliamentary election in 2011, there was finally a chance to make electoral reforms. The coalition government established by the Conservative Party and the Liberal Democratic Party submitted an electoral reform proposal to adopt alternative vote system, and decided to hold a referendum on changing the electoral system. The referendum was held in May of 2011; however, the result is that the proposal was not approved. This paper aims to review the reasons why the electoral reform in the UK failed when originally there seemed to be the possibility to change the electoral system. The paper illustrates the constituent of the alternative vote and the possible effects it would have, analyzes the reasons why the government in the UK proposed alternative vote system rather than other options for electoral reform, and explains the result of the referendum. From the failure of the UK’s electoral reform, we can see that even if the party system is confined by the current electoral system, it still has a chance to get rid of the restraint of the current electoral system and change. In the UK, the two-party system has been molded and confined by FPTP over a long period of time. As a result, the electoral system makes it difficult for small parties to survive. Nevertheless, in the parliamentary election in 2010, the exceptional phenomenon where none of the parties received more than half of the total seats occurred under FPTP, and it prompted the Liberal Democratic Party to face the problem and attempt to change the electoral system. However it did not succeed in the long run. Even though the electoral reform ended with failure, with the increase in votes and seats that small parties get now and the current unstable two-party system, there is still a great possibility that none of the parties will have more than half of the total seats after a future parliamentary election, and, in all likelihood, electoral reform will emerge again.