‘The Nations are one because the Churches are two.’ (Macaulay on the Union of England and Scotland)
These words remind us that, whatever other factors led to the Act of Union 1707, the Union was partly in the nature of a religious settlement. In the previous century, England and Scotland had each tried to impose its own preferred religious system on the other, with disastrous consequences. While the Act of Union united the secular states of England and Scotland, their respective ecclesiastical states remain strictly separate and independent of each other.
The most visible constitutional difference between the Churches of England and Scotland is that the former retains an episcopal structure derived from the late mediaeval Catholic Church, while the latter has a presbyterian structure devised in the early modern period. However, the other important constitutional difference concerns the relationship of the two Churches to the secular state.
The Church of Scotland Act 1921 now defines the boundary between Church and secular state in Scotland. It asserts the autonomy of the Church in ‘matters spiritual’. These matters are specified in the ‘Declaratory Articles’ of the Church, which are scheduled to the Act. According to Article 4 they include ‘all matters of doctrine, worship, government and discipline in the Church, including … [Church] membership and office … and the mode of election of its office-bearers’. Article 4 asserts that the spiritual authority of the Church is ‘subject to no civil authority’, and that the civil authority has no ‘right of interference’ in spiritual matters.
This spiritual autonomy is effected by disapplying or nullifying inconsistent secular laws. Thus s.1 of the 1921 Act provides that
 ‘no limitation of the [Church’s] liberty, rights and powers in matters spiritual … shall be derived from any statute or law … at present in force’
 ‘all such statutes and laws insofar as they are inconsistent with the Declaratory Articles are hereby repealed and declared to be of no effect’ and
 such laws as are not nullified under  are to be ‘construed in conformity … with [the Articles] and in subordination thereto’.
S.1 is a remarkable provision, requiring that certain secular laws are subordinate to ecclesiastical laws. The contrast with English ecclesiastical law could hardly be greater. While English law is concerned to assert the supreme authority of the Monarch over the Church, the 1921 Act and the Declaratory Articles assert the independence of the Church from the Monarch.
Colin Munro observes that ‘The  Act … [is] a recognition by Parliament of the Church’s constitution, rather than as a conferment of a constitution’ (emphasis supplied). It recognises ‘a co-ordinate jurisdiction of Church and state, each supreme within its own sphere’. The Act ‘may be regarded … as … a concordat which allowed that the Church had its own sphere of jurisdiction’ (‘Does Scotland have an Established Church?’, Ecclesiastical Law Journal 1996-7, vol 4, p.639, pp.644).
The Church is described by Article 3 as ‘a national Church representative of the Christian faith of the Scottish people’. The basis of its authority is explained by Article 4, which states that ‘This Church, as part of the Universal Church wherein the Lord Jesus Christ has appointed a government in the hand of Church office-bearers, receives [spiritual authority] from Him … and from Him alone’.
Thus, while the Monarch is the head of both the ecclesiastical and the secular state in England, in Scotland she is head of the secular state alone. Christ is the only head of the Scottish ecclesiastical state.
The governance of the Scottish Church is described in a most helpful modern commentaryThe Constitution and Laws of the Church of Scotland edited by James L Weatherhead(Edinburgh, 1997).
Weatherhead’s account suggests that the Scottish ecclesiastical constitution harks back to the time when all sovereign authority had a judicial character. It does not recognise the modern principle of the separation of legislative, executive and judicial powers, and barely recognises the distinction between these powers (p.88).
Therefore the Church is governed by ‘a conciliar sytem of superior and inferior courts’ (p.97), namely,
(1) the General Assembly
(2) Presbyteries and
(3) Kirk Sessions.
The General Assembly can decide cases both at first instance and on appeal, as can a Presbytery. Kirk Sessions are first instance courts only. There can be no independent review of a decision of the General Assembly. As supreme court, the Assembly is the final interpreter of its own legislation (p.75).
Despite the judicial character of its constitution, the Church of Scotland has no judges, in the sense of legally-qualified officials empowered to decide cases. Judges, like bishops, were distrusted as the agents of royal intervention in ecclesiastical affairs.
Thus, when exercising their judicial function, the Church courts resemble grand juries or committees of magistrates. They are staffed by legally-qualified clerks, procurators and assessors, but these officials, like justices’ clerks, may only give legal advice, not definitive rulings.
The courts are chaired by moderators. Moderators, like Lord Mayors, are elected and hold office for a year. A court may delegate a responsibility to a committee or official.
The Monarch sends a representative, the Lord High Commissioner, to meetings of the General Assembly. His visits are attended with some pomp and circumstance, and he observes the proceedings seated on a throne, as befits his viceregal dignity. However, the Lord High Commissioner ‘has no authority of any kind over the Assembly’ (p.189). The throne is strategically placed just outside the Assembly, to emphasise the separation of Church and state.
It is sometimes glibly remarked that the Monarch is an Anglican in England and a Presbyterian in Scotland. This is not really accurate. The Monarch is obliged by the (English) Act of Settlement 1700 to ‘join in communion with the Church of England’ (s.3), but there is no equivalent obligation in Scottish law. As we have seen, the Monarch is not the Head of the Scottish Church. The only basis for the Monarch’s ‘presbyterianism’ is that she chooses to attend divine service in her local kirk when resident in Scotland. This follows the practice of Queen Victoria, the first Monarch of the United Kingdom to live in Scotland. The practice is purely a matter of personal choice or family tradition. It has no constitutional basis. However, it may have the political effect of softening the separatist and republican character of the Church of Scotland.
The Scottish constitution reminds us that the Church of England is not the only established Church of the United Kingdom, and that a Church may be established by law even if the Monarch or other Head of State is not in communion with it. It shows that ecclesiastical ‘establishment’ is not a uniquely Anglican phenomenon.
The Quebec Act 1774 shows that ‘establishment’ is not uniquely Protestant either. S.5 of the 1774 Act provided that, ‘for the more perfect security and ease of [their] minds … his Majesty’s subjects, professing the religion of the Church of Rome of and in the said Province of Quebec, may have, hold, and enjoy, the free exercise of the religion of the Church of Rome, subject to the King’s supremacy … and that the clergy of the said Church may hold, receive and enjoy their accustomed dues and rights, with respect to such persons only as shall profess the said religion’.
Phillimore admitted (perhaps with a hint of regret) that ‘This Act must be holden to recognize the Church of Rome as an, if not the, Established Church of Lower Canada’ (Ecclesiastical Law, 2nd ed 1895, p.1791). The Quebec Act ensured that Canada remained loyal to the Crown when the American revolution broke out two years later, and never joined the United States. Canada is now an independent country, of course, but it remains a monarchy within the Royal Commonwealth. Tragically, the enlightened religious policy followed in Scotland and Canada was never applied to Ireland.
There may be a certain similarity between the Anglo-Scottish Union and the modern European Union in their treatment of ecclesiastical matters. Much of the governance of the secular state is now regulated by European law, but the ecclesiastical states of both England and Scotland continue to be regulated exclusively by their own domestic laws.