The Miller Respondents, the Lord Advocate on behalf of the Scottish Government, and the applicants in the Northern Ireland judicial reviews of Agnew and others and Raymond McCord all made submissions today. The submissions furthered a number of the arguments made by Lord Pannick yesterday, and dealt with issues of devolution.
However, it was the Supreme Court Justices themselves who provided the most interesting developments today, questioning whether:
a) referenda should now have some constitutional status in the United Kingdom that has until now not formally been recognised;
b) the debate on an Opposition day motion, which asks MPs to "respect the wishes of the United Kingdom" and "calls on the Government to invoke Article 50 by 31 March 2017", in Parliament this evening, if passed, precludes the need for legislation; and
c) it was the role of the Supreme Court to instruct Parliament to introduce Bills, or to adjudicate on the effectiveness of Parliamentary process.
On the role of referenda in the constitution, Lord Neuberger, the President of the Supreme Court, said it would be"a bit surprising that, in a flexible constitution, an act such as the [European] Referendum Act  and an event such as the referendum has no effect as a matter of law". Lord Sumption suggested that the Respondent's argument, based on the writings of A. V. Dicey, a Victorian legal scholar who will be familiar to many law students, that the only legal right of the peopleunder the UK constitution is to elect Members of Parliament "needs to be modified…in an age of referenda". Lord Price added, that life had "moved on" since the time of Dicey: referenda were the people's instructions and must be respected.
The statements are significant. If the Justices consider that referenda are now endowed with a legal status, which has not previously been granted to them (according to traditional conceptions of the UK constitution), the Supreme Court is likely to find it easier to decide in favour of the Government.
This led the Court to question its own role under constitution. If Parliament had decided not to legislate on a matter, was it the Supreme Court's place to instruct Parliament on how to exercise its sovereignty?
Lord Reed argued that it would be "constitutionally a novelty" if the Court compelled Parliament to consider passing legislation. In light of today's debate in the House of Commons, Lord Reed went on to suggest that if Parliament were to "pass a resolution in both Houses approving of notification" the Court could not subsequently instruct Parliament that only an Act of Parliament would suffice.
Lords Sumption and Kerr disagreed. Lord Sumption said that only Acts of Parliament can change the law; resolutions were political acts that did not affect the Court's decisions. Lord Kerr suggested that, in the event that the Supreme Court was to find that legislation was required for the Government to give notification under Article 50, it would not be telling Parliament what to do. Rather, it would be ruling the extent of the Government's power, something that the Supreme Court is entitled, if not duty-bound, to do. Unsurprisingly, the Respondent's agreed with Lord Kerr's assessment.
The case continues into its final day tomorrow. Read this morning's transcript here.