On Day 1 (5th December) - transcript here - James Eadie QC (for the government) referred early in his submissions to an article on the prerogative by Professor Endicott (Balliol College, Oxford). I believe that the article referred to was dated 1st December 2016 - Parliament and the Prerogative: from the Case of Proclamations to Miller.
An article written by Lord Millett (supportive of the government's position) gets a mention at page 42 and Lord Millett's "concept of inherency" is referred to again at page 46 and at page 132 Eadie says that the government adopts Millett's analysis at a "more fundamental level." The court returned to Millett on Day 2 - transcript at pages 42 and 43. (Lord Millett - Lord of Appeal in Ordinary 1998 to 2004).
Eadie QC also referred to what the Foreign Secretary had said during the House of Commons second reading on the Referendum Bill - see Day 1 transcript at page 5 and also page 161 at lines 19 to 23.
Professor Finnis (also Oxford) receives mention for an article at page 49 and for a lecture at page 95. In the government's written case, an article by Finnis and published on the UK Constitutional Law Association blog (together with a supplementary note) is referenced on page 22 - Terminating Treaty-based UK Rights and supplementary note.
Other citations in the government's written case include Professor Tomkins (pg 25); Professor Mark Elliott and Hayley Cooper (pg 26) and Professor Feldman (pg 27).
The fact is that there was an absolute plethora of material published in advance of the case - I collected links to quite a lot of it - HERE. The UK Constitutional Law Association blog has dozens of articles and the reader (or court?) could take its pick as to which to read. Many are from legal scholars and the opinion is by no means confined to the Universities of Oxford and Cambridge.
With regard to allowing in matters said in Parliament, the leading modern authority is the decision of the House of Lords 24 years ago in Pepper v Hart permitting certain parliamentary statements to be given in evidence to resolve an ambiguity. See the transcript for 7th December, to read a brief exchange between Lord Pannick QC and Lord Neuberger - at page 4 line 3 to page 6 line 17. Lord Neuberger said to Lord Pannick: - "The only trouble with looking at what was said on the floor of the House, and as you say, we don't want to go too much into this, is what a minister or somebody else says does not necessarily represent the reason why people vote, or what they believe when they vote. It is like going into what people say about their contracts when construing their contracts, and that way madness can be said to lie, because you then start looking at everything said in Parliament and balancing up -- it can be a very treacherous course."
Pepper v Hart also arose toward the end of submissions by Mr Dominic Chambers QC in the Brexit litigation. On this see the Transcript of the Supreme Court hearing at pages 108-111 - Morning and afternoon combined - 4 page version (PDF)
(For further, see Note 1 below).
Then we come to historical materials. An example is that both Magna Carta 1215 and the Declaration of Arbroath 1320 appear in the written argument put by the Independent Workers Union of Great Britain - (page 3). This submission refers to " .... the Scottish tradition, since at least the Declaration of Arbroath 1320, of the sovereignty of the people limiting the powers and rights of the Crown (and Parliaments)" This seems to be a somewhat vague notion and older documents such as Arbroath are open to various interpretations. From my reading of the Scots Constitutional Law textbook by J D B Mitchell - Constitutional Law (2nd Edition 1968) - I have not been able to find support for a doctrine of "People sovereignty" in Scotland as opposed to Parliamentary sovereignty belonging to the UK Parliament and the learned author devoted an entire chapter to the latter. (The Parliament of the single Kingdom of Great Britain was formed by the Acts of Union 1706 and 1707 - see Note 2 below). I would certainly be interested in alternative views on this but please support them by authorities such as decided cases etc. Of course, in a representative democracy, the people have the ultimate say in who they elect to Parliament. The UK Parliament has one elected House (Commons) and one not elected (Lords). The Scottish Parliament and the Assemblies for Wales and Northern Ireland are fully elected.
Furthermore, if a referendum is held then the outcome of that referendum must have political impact but its legal impact is another matter and will depend essentially on the legislation enabling the referendum to take place. Here the contrast between the European Union Referendum Act 2015 and the Parliamentary Constituencies and Voting Act 2011 is very marked. The former did not address what was to happen if there was a Leave vote. The latter positively addressed the actions to be taken if the voters had opted for the Alternative Vote system.
I have no idea whether the Justices of the Supreme Court have read all of the material referred to in the written cases and in the oral hearing. They each have an extensive bundle extending to over 30,000 pages (or the electronic equivalent)! As decision-makers, the justices will no doubt focus into the key points in the case and even the most complex cases ultimately boil down to what really has to be addressed to reach a final conclusion. The wheat will be sorted from the chaff and the wood will appear from the trees! It will be fascinating to see just how much of the material presented finds its way into the final judgment(s).
1. The extent to which courts refer to material used by Parliament is a considerable topic. Historically, the courts did not look at such material. As Lord Cooper noted in the Scottish case of MacCormick v Lord Advocate:
"Parliament can only speak through the medium of a statute. A court of law is not entitled to investigate the Parliamentary history of a Bill ..."
The speeches in Pepper v Hart trace the background to the similar rule that existed in England - Davis v Johnson [1979[ AC 264. The change made by Pepper v Hart was expressed by Lord Browne-Wilkinson as:
"In my judgment, subject to the questions of the privileges of the House of Commons, reference to Parliamentary material should be permitted as an aid to the construction of legislation which is ambiguous or obscure or the literal meaning of which leads to an absurdity. Even in such cases references in court to Parliamentary material should only be permitted where such material clearly discloses the mischief aimed at or the legislative intention lying behind the ambiguous or obscure words. In the case of statements made in Parliament, as at present advised I cannot foresee that any statement other than the statement of the Minister or other promoter of the Bill is likely to meet these criteria."
2. The sovereignty of Parliament. The dictum of Lord Cooper in MacCormick v Lord Advocate is often quoted when he said that - "The principle of the unlimited sovereignty of Parliament is a distinctively English principle which has no counterpart in Scottish constitutional law....."
Lord Cooper had difficulty in seeing why the new Parliament of Great Britain had inherited all the peculiar characteristics of the former English Parliament but none of the former Scottish Parliament. Later, Lord Cooper noted:
"I have not found in the Union legislation any provision that the Parliament of Great Britain should be "absolutely sovereign" in the sense that that Parliament should be free to alter the Treaty at will."
However, even if it is accepted that there are provisions in the Treaty of Union and associated legislation which are "fundamental law" a question of justiciability would exist if it were said that something had been done in breach of such a fundamental law.
The background to the Acts of Union between Scotland and England is interesting and was discussed in the House of Lords in Lord Grey's Motion  UKHL 53.
In Scottish Parliamentary Corporate Body v The Sovereign Indigenous Peoples of Scotland, Lord Keith’s opinion in the case of Gibson v Lord Advocate 1975 SC 136 was noted: Lord Keith said:
“I am, however, of opinion that the question whether a particular Act of the United Kingdom Parliament altering a particular aspect of Scots private law is or is not “for the evident utility” of the subjects within Scotland is not a justiciable issue in this Court. The making of decisions upon what must essentially be a political matter is no part of the function of the Court, and it is highly undesirable that it should be. The function of the Court is to adjudicate upon the particular rights and obligations of individual persons, natural or corporate, in relation to other persons or, in certain instances, to the State. A general inquiry into the utility of specific legislative measures as regards the population generally is quite outside its competence.”