The Union of England and Scotland in 1707 is a fascinating moment in terms of the doctrine of Parliamentary sovereignty, there are two reasons for that. The first is that the Union in some senses has been taken in the past to limit British Parliamentary sovereignty- some have argued that the Union has the authority of a British constitution or a treaty between two international partners. The second, which I will discuss here, is whether the Scottish Parliament ever had the authority to sign the articles of union and subsume itself within a British Parliament. The arguments between those who believed that the Parliament could or could not deal with the English Parliament concentrated on what powers a Parliament might have- they came in the end down to status of the Scottish Parlaiment as it might dispose of property.
Essentially what we have in 1707 is an argument about the rights of property in a new union. There were broadly three positions that Scots took within this argument. For some like Robert Wyllie and earlier Sir George MacKenzie the Scottish Parliament could not overturn property rights on its own- and property rights included the right to vote and the right to be represented. As the Scottish Parliament could not do this, Wyllie demanded a referendum, MacKenzie suggested that every Scottish MP be accorded the right to veto the legislation should he so choose. A second answer came from Francis Grant (later elevated to the bench as Lord Cullen). Grant argued that the Scottish Parliament could not alter the rights under which Scots lived- but could like a landowner who bequeathed his estate through an entail which limited the rights of disposal of his heir- limit what the British Parliament might do to Scotland. The fact of inheritance in Cullen's mind changed the nature of Parliamentary power- it created a limited power for Parliament within Scotland.
Those were not the only arguments available to unionists though in 1707. The last argument was made by a group of theorists including the Earl of Cromarty, William Seton of Pitmeddon and David Symson and its implications for what a UK Parliament might do were revolutionary. Seton, Cromarty and Symson suggested that the Scottish Parliament was a sovereign body- what distinguished it from any other assembly was not its representative nature but its powers. Its powers meant that it could alter or dispose of the Scottish constitution and indeed of Scotland as it chose. Symson evoked the idea of eminent domain, borrowed from the Dutch political theorist Hugo Grotius- the argument that for the public benefit the sovereign could decide to annex and use any piece of land or property whatever the wish or right of the previous owner was. Using this argument, Symson argued that though the Scots had rights to representation in a Parliament, that Parliament might dilute them in any way it chose. Similarly Cromarty denied that there was any way in which sovereignty might be held to account for the actions it chose: if it was held to account, it would (he argued immitating Hobbes) not be sovereign. Seton agreed completely, rejecting the argument that Scotland was like a Poland an aristocratic confederation or a democratic government.
These last two arguments, about the competence of the Scottish Parliament, were the arguments most harkened to by politicians in 1707. The first of them- that the Scottish Parliament bequeathed to England a country by entail has disturbing implications- it implies for a start that Scotland, as some argued, might be a different constitutional entity within the United Kingdom from England. The second argument though is equally disturbing and interesting. Suggesting with Cromarty and Seton and Symson that the Parliamentary union of 1707 depends on the assumption that the Crown in Parliament has untramelled sovereignty to dispose as it wishes creates an unsettling thought: that the United Kingdom's Parliament may be a Hobbesian sovereign. In a sense it moves us to the real issue underlying all of this argument: the Union of 1707 was a device in part to stop the reemergance of religious warfare in the UK (through the accession of the Stuarts in the North of the island and the Hanoverians in the South)- it was part of a settlement that was created between 1688 and 1715 which created the modern British Protestant state.
Perhaps a secret about that state is that its creation involved the acceptance of untrammelled Parliamentary authority and perhaps when we discuss that state we ought to be more aware of the shadowy ghost of Thomas Hobbes stalking behind us. Perhaps, if Seton and Symson and Cromarty were right, the Parliamentary union between England and Scotland represented the solution to the problems of the 1640s: to avoid an arbitrary Catholic monarch, the United Kingdom became (for a time) an arbitrary Parliamentary dictatorship.