On 24 September 2019, in a unanimous judgment the UK Supreme Court ([2019] UKSC 41) ruled that the Prime Minister's action to prorogue (suspend) Parliament for 5 weeks in the run-up to the 31-10-2019 deadline of the UK leaving the European Union, was unlawful and of no effect, as it prevented Parliament from carrying out its constitutional functions without reasonable justification. Although the Court did not pronounce on the merits and demerits of Brexit, its decision delighted "Remainers" but appalled "Leavers". The Court ruling epitomises the potency of constitutional review by an independent judiciary. The paper applies collective choice theory to analyse the ruling of the Supreme Court. This is accomplished by (a) examining the legal basis of the Court ruling; (b) reviewing arguments for judicial review and (c) exploring the effect of the Court as an additional player in the game of collective choice in a spatial decision model. Keywords Prorogation of Parliament • UK Supreme Court • Separation of powers • Constitutional judicial review • Judicial independence • Veto players JEL classification D72 • D74 • D78 • K40 • K41 "[I]t is…of course true…that Parliament, the executive and the courts have different functions. But the function of independent judges charged to interpret and apply the law is universally recognized as a cardinal feature of the modern democratic state, a cornerstone of the rule of law itself." Lord Bingham, A and others v Secretary of State for the Home Department [2004] UKHL 56