The inability of the Conservative Government led by Prime Minister Theresa May to deliver a Brexit deal by 29 March 2019 was a policy fiasco, condemned widely by Remainers and Leavers alike. The entire process was a unique combination of chaos, day-by-day unravelling of new proposals and gridlock. This article examines three main explanations for the fiasco that are prevalent in contemporary political discourse. Analysis is underpinned by conceptual literature straddling policy fiascos and policy studies. It examines three explanations (i) Brexit as an impossible policy challenge (ii) ineffectual leadership by Theresa May who took poor decisions and avoided plausible alternatives and (iii) Westminster as a partisan-fuelled institution incapable of reaching agreement on such a bi-partisan issue. The article concludes by considering whether any single explanation is sufficiently plausible, situating this analysis within long-standing debates on the nature of UK politics. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.