On 24 September 2019, in a unanimous judgment the UK Supreme Court 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. [---] 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.