本文旨在介紹公民投票制度於英國憲政體制中之發展，並以近年兩次的重要公投－2014年的蘇格蘭獨立公投以及2016年舉行的歐盟公投爲主要觀察對象。本文首先針對英國辦理公民投票之法制架構予以探究，以說明於英國辦理公民投票之法制基礎，並且說明英國憲政上的「議會主權觀」是理解英國的公民投票制度與其他歐洲國家有相當差異的核心，其後，本文分別簡要說明兩次公投之過程以及其間所浮現的法律爭議，以說明其所凸顯出藉公民投票處理可能涉及國際事務的侷限性。綜言之，本文認縱使基於不成文憲法、議會主權之憲政體制，加上充分尊重民主精神、容許不同政治意見充分表達之環境下，使得即使是獨立公投此種一般國家尚難容忍之公投，在英國亦成為可能。然而，兩次公投也充分反映不同主權觀間相互影響的複雜關係。而縱然英國在國內層次能透過政治素養、法制安排及最高法院釐清等手段解決可能衝突與矛盾，但這種憑藉個案安排解決問題所導致的不確定性，除使公民投票的辦理存有障礙外，更可能根本侵蝕憲法秩序下的明確性與安定性。又縱然英國最高高法院在米勒案中再次確立議會主權在英國之重要性，然而，實踐上已經顯示，在處理對外關係上，想依公投結果盡如己意，有其困難。就此，與其說是公民投票之侷限，毋寧更可能要說是民主的可能極限－在國際法上對於民主決定並無必然等重之要求下，公民投票縱使給可能給予國內民眾無限想像，但恐非處理對外關係之尚方寶劍，甚至可能因此反挫人民對於民主之信賴，頗值深思。

As one of the papers presented in a symposium introducing referendums in European states, this article took the 2014 Scottish Independence Referendum and 2016 European Union Membership Referendum as the examples to illustrate the theory and practice of referendums in the British context, and to further consider the implications reflected from the referendums. It argued that even if the United Kingdom could solve legal and political controversies arising from referendums with their constitutional order as well as their political culture, yet the case-by-case approach would risk the constitutional order with ambiguity and uncertainty. Moreover, even if the Supreme Court of the United Kingdom has reiterated the importance of parliamentary sovereignty in its Miller Case, the public will reflected from the referendums could by no means be projected to the international arena easily and smoothly, particularly at a time when democracy is yet an emerging idea in international law. Considering that this shortcoming may further undermine the voters' belief in their own domestic constitutional democracy, as conclusion, this article argued that a referendum is unlikely the ideal mechanism for solving matters of international nature.