James Bogle acted in the “BREXIT case”, for the 5th Intervenor, to argue that the Executive had the power, under the Crown’s prerogative, to give notice pursuant to TEU art. 50(2) for the UK to withdraw from the EU without the need for any further act of Parliament than the Referendum Act 2015, such being the case with other treaties from which the Executive had withdrawn, even when domestic treaty-based rights were thereby affected. The Secretary of State appealed against a decision of the Divisional Court and the Supreme Court permitted other parties to intervene. Devolution questions were raised on a further appeal against a decision that the constitutional arrangements for Northern Ireland did not affect the Government’s power to give notice under art. 50(2). In this landmark constitutional case, the Supreme Court held that an Act of Parliament was, in fact, needed before the Executive could give notice under art. 50 and the various devolution questions were answered in the negative. However, citing in part arguments of the 5th intervenor, Lords Reed, Carnwath and Hughes dissented as to the need for an Act of Parliament prior to the giving of art. 50 notice.
R (Miller and anor) v Secretary of State for Exiting the European Union, UK Supreme Court,  UKSC 5 (Lord Neuberger, President, Lady Hale, Deputy President, Lords Mance, Kerr, Clarke, Wilson, Sumption, Reed, Carnwath , Hughes and Hodge).