Labour seeks to amend the EU Withdrawal Bill so that parliament must vote on the terms of the exit agreement, and, if it rejects those terms, that the UK shall not leave the EU without a further parliamentary vote. The rationale for this position is the familiar idea of parliamentary sovereignty. We live, say its champions, in a system not of direct democracy but of parliamentary democracy: parliament has, over the centuries, beaten off threats from a series of totalitarian challengers (today, ‘populism’) and emerged as the champion of the ‘rights of Englishmen’ or, as the dominant political language now has it, of ‘universal human rights’. Parliament, consequently, is sovereign.

This sounds grand in the House of Commons or Supreme Court, but is poor history. The idea was always rhetoric, with good or bad consequences according to taste. Historically, successive institutions or groups exercised considerable power, and so laid claims to ultimate sovereignty; these claims clashed, and were never finally settled. Indeed, there is no finality in politics or jurisprudence, no ‘fundamental law’.

After the fall of Rome, the Catholic Church became a leading player. For one period of its history it claimed jurisdiction over secular princes. The high point of its European integrationist idealism was the humiliation of Holy Roman Emperor Henry IV by Pope Gregory VII at Canossa in 1077. But the meaning of those events was far from unambiguous, and the ideological balance between church and state continued to fluctuate.

The Reformation tilted that balance: as the Church was torn apart the winners were the princes, claiming to rescue the people from the wars of religion that the Reformation unleashed. But no sooner had the princes achieved dominance than Protestantism empowered ever more subjects to dispute the absolute sovereignty of the monarch. Civil war, not consensus, followed.

When a weakened monarchy was restored in England in 1660 the chief winners were less ‘the people’ acting via the House of Commons than the nobility. Especially after a second blow to the idea of monarchical sovereignty with the expulsion of James II in 1688, the Whig peers presented the House of Lords (that is, themselves) as the chief principled barrier against an over-mighty crown. Even then the crown held some real power until the Reform Bill of 1832, and the Lords retained residual authority until the Parliament Act of 1911.

In the nineteenth century Whiggish constitutional lawyers like A. V. Dicey began to trumpet the idea of parliamentary sovereignty: it was said that parliament was so powerful that it could do anything except turn a man into a woman or a woman into a man.

No sooner had this creed seemed orthodoxy than it was challenged in turn. The movement for Irish independence provoked Dicey to argue that if parliament voted for Home Rule, the Bill might be reversed by a referendum. Meanwhile, another power was rising in the land: the press lords, dominating the new mass media.

Universal suffrage strengthened their claimed authority to speak for popular sovereignty; but this claim was contested in turn by politicised trades unions, reaching their apogee in Edward Heath’s defeat in 1974. Yet no sooner had Margaret Thatcher seen off the unions than the reasserted sovereignty of House of Commons was overridden by first a trickle, then a flood, of secondary legislation from Brussels; legislation that parliament was compelled merely to rubber stamp and UK courts to implement.

Into this constitutional arena another wild beast is now released: the referendum. The greatest changes are often unintended: ironically, this political revolution was a consequence of the EU-inspired referendum in 2004 on a regional assembly for the North East. As we now appreciate, the implication of a binding referendum (as the then ministry advertised the EU referendum of 2016) was that the sovereignty of parliament might ultimately be trumped by the sovereignty of the people.

The MPs who were formerly the most complicit in this erosion of Westminster’s power and authority now protest most loudly in defence of the slogan of parliamentary sovereignty when the executive labours to withdraw the UK from the jurisdiction of the European Court of Justice. Such Remainers have already made it impractical, for the present at least, to extricate the UK from the jurisdiction of the European Court of Human Rights; they may do the same for the jurisdiction of the ECJ.

Some may stigmatise their conduct as hypocrisy, but we need a non-partisan analysis of what is going on. An historian might suggest that ‘sovereignty’ was never a finite something that could be measured, or even (as Geoffrey Howe implied in his famous resignation speech) shared with a supra-national organisation. Sovereignty is, rather, an ideal which many players in the political arena invoke.

New claimants continually arise. Now another consequence of Blairite Euro-idealism manifests itself: the devolved assemblies of Edinburgh and Cardiff, or some of their members, begin to claim to exercise not merely devolved power, but the ‘sovereignty’ of their ‘nations’.

These claims can never have final, definitive, answers. They were always rhetorical ploys intended to justify the capture and exercise of power. What one thinks of them is dependent on one’s opinion of the policy goals which they serve. The Labour Party of Jeremy Corbyn and John McDonnell professes its regard for democracy and the House of Commons, but its practice might be summed up as the subordination of that House to the ‘power of the streets’, to informal mass action: a different sovereignty.

The art of politics is to manage the competing claims of new groups, practices, and ideologies. Today, the challenge is to accommodate the rising power of popular involvement, expressed in referendums. Significantly, some Labour Remainers pin their hopes on a second referendum, not a parliamentary vote. Will the Commons emerge as ‘sovereign’? Constitutionally, nothing is decided until everything is decided, and in politics it never is. As before, a reassuring phrase may mask a variety of outcomes. But the opposition cannot claim to have ‘the constitution’ on its side.