The clause in the Treaty of Union by which Scottish representative peers sat in the House of Lords is a fundamental constitutional law which Parliament has no legal authority to over-ride. Any Act of Parliament which purports to over-ride any clause of the Treaty is null and void.
This matter is explained more fully in an article of June 2007 by David M Walker, Regius Professor of Law at the University of Glasgow 1958-1990, in The Journal of the Law Society of Scotland, 'The Union and the Law'. As he says in that article 'In his judgment in McCormick v Lord Advocate 1953 SC 396 Lord President Cooper, admittedly obiter, observed that the principle of the unlimited sovereignty of the Westminster Parliament was a distinctively English principle which had no counterpart in Scottish constitutional law. In particular the Lord Advocate had conceded in that case that the Parliament of Great Britain could not repeal or alter fundamental and essential conditions of the Treaty and associated legislation' which means that the unalterable nature of the Treaty has been acknowledged by the principal law officer of the Crown in Scotland.
Note that the British government still holds that the Treaty of Utrecht of 1713, by which Spain ceded Gibraltar to Great Britain, is binding in law. See the statement made in the House of Commons on 27 March 2006 by the then Secretry of State for Foreign and Commonwealth Affairs that 'I will note that, in the view of Her Majesty's Government, Gibraltar's right of self determination is not constrained by the Treaty of Utrecht except in so far as Article X gives Spain the right of refusal should Britain ever renounce Sovereignty. Thus independence would only be an option with Spanish consent.' If the rights of the United Kingdom with respect to Gibraltar are constrained by the Treaty of Utrecht of 1713, then are not the rights of the United Kingdom with respect to Scotland also constrained by the Treay of Union of 1707? Either such treaties are binding in law or they are not. Which is it?
In the judgment in McCormick v Lord Advocate 1953 SC 396 Lord President Cooper stated 'Further, the Treaty and the associated legislation, by which the Parliament of Great Britain was brought into being as the successor of the separate Parliaments of Scotland and England, contain some clauses which expressly reserve to the Parliament of Great Britain powers of subsequent modification, and other clauses which either contain no such power or emphatically exclude subsequent alteration by declarations that the provisions shall be fundamental and unalterable in all time coming, or declarations of a like effect.' (as quoted in Hansard 27 Jul 1999, Column 1422).
See also Jackson & Ors v. Her Majesty's Attorney General [2005] UKHL 56, a House of Lords case binding on all lower courts, where reference was made to Bribery Commissioner v Ranasinghe [1965] AC 172 where the Privy Council stated at p. 197-8: 'A legislature has no power to ignore the conditions of law-making that are imposed by the instrument which itself regulates its power to make law. This restriction exists independently of the question whether the legislature is sovereign, as is the legislature of Ceylon, or whether the constitution is 'uncontrolled,' as the board [in McCawley'scase [1920] AC 691] held the constitution of Queensland to be. Such a constitution can, indeed, be altered or amended by the legislature, if the regulating instrument so provides and if the terms of those provisions are complied with: and the alteration or amendment may include the change or abolition of those very provisions. But the proposition which is not acceptable is that a legislature, once established, has some inherent power derived from the mere fact of its establishment to make a valid law by the resolution of a bare majority which its own constituent instrument has said shall not be a valid law unless made by a different type of majority or by a different legislative process.'
See also Jackson & Ors v. Her Majesty's Attorney General [2005] UKHL 56 at 106 and 107 where Lord Hope of Craighead said: 'It has been suggested that some of the provisions of the Acts of Union of 1707 are so fundamental that they lie beyond Parliament's power to legislate. Lord President Cooper in MacCormick v Lord Advocate, 1953 SC 396, 411, 412 reserved his opinion on the question whether the provisions in article XIX of the Treaty of Union which purport to preserve the Court of Session and the laws relating to private right which are administered in Scotland are fundamental law which Parliament is not free to alter. Nevertheless by expressing himself as he did he went further than Dicey, The Law of the Constitution, 10th ed (1959), p 82 was prepared to go when he said simply that it would be rash of Parliament to abolish Scots law courts and assimilate the law of Scotland to that of England. In Gibson v Lord Advocate, 1975 SC 136, 144, Lord Keith too reserved his opinion on this question and as to the justiciability of legislation purporting to abolish the Church of Scotland. In Pringle, Petitioner, 1991 SLT 330, the First Division of the Court of Session again reserved its position on the effect of the Treaty of Union in a case which had been brought to challenge legislation which introduced the community charge in Scotland before it was introduced in England. But even Dicey himself was prepared to recognise that the statesmen of 1707 believed in the possibility of creating an absolutely sovereign legislature which should yet be bound by unalterable laws: Thoughts on the Scottish Union, pp 252-253, quoted by Lord President Cooper in MacCormick at p 412. So here too it may be said that the concept of a Parliament that is absolutely sovereign is not entirely in accord with the reality. Nor should we overlook the fact that one of the guiding principles that were identified by Dicey at p 35 was the universal rule or supremacy throughout the constitution of ordinary law. Owen Dixon, "The Law and Constitution" (1935) 51 LQR 590, 596 was making the same point when he said that it is of the essence of supremacy of the law that the courts shall disregard as unauthorised and void the acts of any organ of government, whether legislative or administrative, which exceed the limits of the power that organ derives from the law. In its modern form, now reinforced by the European Convention on Human Rights and the enactment by Parliament of the Human Rights Act 1998, this principle protects the individual from arbitrary government. The rule of law enforced by the courts is the ultimate controlling factor on which our constitution is based. The fact that your Lordships have been willing to hear this appeal and to give judgment upon it is another indication that the courts have a part to play in defining the limits of Parliament's legislative sovereignty.' See also AXA General Insurance Ltd & Ors v. The Scottish Ministers & Ors [2011] ScotCS CSIH 31 at 62 et seq.
In Whaley v Lord Watson 2000 SC 340 Lord Prosser said at pp. 357-8: 'If and in so far as a parliament may have powers which are not limited by any kind of legal definition, there is no doubt scope for concepts of 'sovereignty', with the courts unable to enforce boundaries which do not exist. But if and in so far as a parliament and its powers have been defined, and thus limited, by law, it is in my opinion self-evident that the courts have jurisdiction in relation to these legal definitions and limits, just as they would have for any other body created by law.'
The binding nature of international treaties as fundamental and unalterable laws in situations where two countries merge or where two peoples agree to live together in one country is illustrated by the United Nations General Assembly Resolution 181 of 29/11/1947 concerning Palestine. This stated that 'The stipulations contained in the Declaration are recognized as fundamental laws of the State and no law, regulation or official action shall conflict or interfere with these stipulations, nor shall any law, regulation or official action prevail over them.' The nature of such treaties is therefore quite clear and, more importantly, internationally acknowledged; they become fundamental and unalterable (i.e. constitutional) laws of the new state and, to that extent, limit the sovereignty of the government of that country, whatever its democratic mandate (which is not to say that such laws cannot be altered but this can only be done with the specific consent of the original parties to the treaty, in so far as they remain identifiable (e.g. Scots and English or Jewish and Arab). Since the whole purpose of such agreements is to protect minority rights, it is a nonsense to allow the majority to negate such agreements simply because they are the majority (which is what the doctrine of the supremacy of parliament effectively does). Only if one of the parties no longer exists or is no longer identifiable would such action be justified, which is not the case in the United Kingdom.
The question of whether the Treaty of Union of 1707 remains binding was considered by the Committee for Privileges of the House of Lords in 1999 before the passing of the House of Lords Act 1999. The issue was whether the Act would contravene article 22 of the Treaty of Union by removing the right of Scottish peers to sit in the House of Lords. The unanimous opinion of the Committee was that it would not, although only the three law lords involved gave their reasons. It is worth considering these reasons briefly. But note, in particular, part of the case for Lord Grey which says (para. 20):
'In respect of the earlier debate on Article III, on 18 November 1706, Defoe records ['History of the Union between England and Scotland', 3rd edtn London, John Stockdale, 1786] that:
"The capital arguments made use of on this occasion . . . were such as these:—
1. That whatever agreement is now concluded between the two kingdoms, will never be binding to the new Parliament.
2. That the two kingdoms effectually subject themselves to the new Parliament, all the conditions stipulated on either side to the contrary in any wise notwithstanding.
To this it was answered, That the British Parliament were absolutely bound up by the stipulations of this treaty; that they being a subsequent power to the two respective Parliaments of either kingdom, had no other or farther power to act than was limited to them by the stipulations of both kingdoms . . . That the Parliament of Britain, being the creature of the Union, formed by express stipulations between the two separate Parliaments of England and Scotland, cannot but be unalterably bound by the conditions so stipulated, and upon which it received its being, name and authority."'
Thus the intention of the Scottish Parliament was made abundantly clear.