The doctrine of parliamentary supremacy is deeply engrained in English law. Jeffrey Goldsworthy has traced it back to Tudor times and beyond (for historical examples, see here, here and here). Yet its status is not as unquestioned or unquestionable as some might think. The leading constitutional scholar Vernon Bogdanor has affirmed: "In practice…if not in law, parliamentary sovereignty is no longer the governing principle of the British constitution". This is an explicitly practical rather than legal statement, but it can be given some legal backing too.
1. Parliament is bound by the Treaty of Union
The Parliament of the United Kingdom is the present-day successor of the Parliament of Great Britain created by Article III of the 1707 Treaty of Union between England and Scotland. The Treaty, which was endorsed by the English and Scottish Parliaments, contains several provisions that purport to be unamendable. It may be argued that it is beyond the power of Parliament to alter these provisions, since Parliament can have no authority to go back and rewrite the document(s) on which its own existence depends. In the practical sphere, it appears that some of the "unamendable" provisions (Scots lawyers disagree about how many) have in fact been amended over the years, but that doesn't mean that the amendments were lawful or that any future such amendments will be accepted so easily.
The Scottish courts appear to be sympathetic to this line of argument. In MacCormick v Lord Advocate 1953 SC 396, Lord President Cooper stated, on behalf of the Court of Session:
The principle of the unlimited sovereignty of Parliament is a distinctively English principle which has no counterpart in Scottish constitutional law.... Considering that the Union legislation extinguished the Parliaments of Scotland and England and replaced them by a new Parliament, I have difficulty in seeing why it should have been supposed that the new Parliament of Great Britain must inherit all the peculiar characteristics of the English Parliament but none of the Scottish Parliament, as if all that happened in 1707 was that Scottish representatives were admitted to the Parliament of England. That is not what was done. 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 provision shall be fundamental and unalterable in all time coming, or declarations of a like effect.... 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.Lord Keith of the Court of Session also considered the issue in Gibson v Lord Advocate 1975 SLT 134:
....I prefer to reserve my opinion what the position would be if the United Kingdom Parliament passed an Act purporting to abolish the Court of Session or the Church of Scotland or to substitute English law for the whole body of Scots private law.Similar comments can be found in Pringle, Petitioner 1991 SLT 330 and in Lord Hope's speech in Jackson v Attorney General  UKHL 56. Halsbury's Laws (8(2), 53) takes an agnostic position:
It is uncertain... whether any provisions in the Treaty of Union are incapable of being amended by the Westminster Parliament and, in that event, whether the validity of any attempt to amend them is a matter that could be decided by the English or Scottish courts....
2. The traditional doctrine is not bulletproof
If some commentators are to be believed, the doctrine of parliamentary supremacy is so integral to the British constitution that it would take a revolution (peaceful or otherwise) to dislodge it. But is this true? It can be argued that parliamentary sovereignty is a creature of the common law. Given that common law is whatever the judges say it is, changing judicial attitudes could spell an end to the traditional doctrine. As Rabinder Singh QC has put it:
[The] doctrine cannot itself be the product of the will of Parliament because that would be circular. In any event there is no Act of Parliament which lays down [the] doctrine. The doctrine therefore appears to be a rule of the common law and, as such, could be altered in the future.This notion has high-ranking judicial support. In Jackson v Attorney General, Lord Steyn commented on parliamentary sovereignty:
It is a construct of the common law. The judges created this principle. If that is so, it is not unthinkable that circumstances could arise where the courts may have to qualify a principle established on a different hypothesis of constitutionalism.Lord Steyn later elaborated on this point in his 2006 Attlee Foundation Lecture by suggesting that the courts may not tolerate infringements by Parliament of "the fundamental principles of our constitutional democracy, such as 5 year Parliaments, the role of the ordinary courts, the rule of law, and other such fundamentals".
3. The doctrine is unreal and leads to absurdities
One of the most famous quotations about parliamentary sovereignty comes from the Victorian philosopher Sir Leslie Stephen, who wrote in The Science of Ethics:
If a legislature decided that all blue-eyed babies should be murdered, the preservation of blue-eyed babies would be illegal; but legislators must go mad before they could pass such a law, and subjects be idiotic before they could submit to it.But if a legal doctrine allows for such absurdities, shouldn't we draw the conclusion that something must have gone wrong somewhere? Lord Denning MR said, famously, in the case of Blackburn v Attorney-General  1 WLR 1037:
We have all been brought up to believe that, in legal theory, one Parliament cannot bind another and that no Act is irreversible. But legal theory does not always march alongside political reality. Take the Statute of Westminster 1931, which takes away the power of Parliament to legislate for the Dominions. Can any one imagine that Parliament could or would reverse that Statute? Take the Acts which have granted independence to the Dominions and territories overseas. Can anyone imagine that Parliament could or would reverse those laws and take away their independence? Most clearly not. Freedom once given cannot be taken away. Legal theory must give way to practical politics.If saying that (for example) Parliament could revoke the independence of Canada is a practically absurd statement, why would we insist on clinging to a legal doctrine that so readily allows us to make it?
4. The case-law gives only equivocal support to the doctrine
It is well known that a number of older cases more or less explicitly deny the principle of parliamentary supremacy. Here is Sir Edward Coke in Dr Bonham's Case (1610) 8 Co Rep 114:
And it appears in our books, that in many cases, the common law will controul Acts of Parliament, and sometimes adjudge them to be utterly void: for when an Act of Parliament is against common right and reason, or repugnant, or impossible to be performed, the common law will controul it, and adjudge such Act to be void.Chief Justice Hobart said in Day v Savadge (1614) Hob 85:
[E]ven an Act of Parliament, made against natural equity, as to make a man Judge in his own case, is void in itself....It was stated in R v Love (1653) 5 State Tr 825:
Whatsoever is not consonant to the law of God, or to right reason which is maintained by scripture,….be it Acts of Parliament, customs, or any judicial acts of the Court, it is not the law of England.And here is Chief Justice Holt in City of London v Wood (1701) 12 Mod Rep 669:
What my Lord Coke says in Dr. Bonham's case... is far from any extravagancy, for it is a very reasonable and true saying, That if an Act of Parliament should ordain that the same person should be party and judge, or what is the same thing, judge in his own cause, it would be a void Act of Parliament.However, Holt also said in his judgment that "an Act of Parliament can do no wrong, though it may do several things that look pretty odd".
About a century later, in a Scottish case (Andrew v Murdoch (1806) Buch Rep 1), Lord Hermand stated in the Court of Session that "there is a power paramount to acts of Parliament, and that is the power of right reason, to which Kings and Parliaments themselves must be subject". This may indicate a freer attitude towards parliamentary supremacy on the part of Scottish lawyers, but it is worth noting that these and other dicta of Lord Hermand were subsequently disapproved by Lord Holland in the House of Lords.
The last case in this line is Forbes v Cochrane (1824) 2 B & C 448, in which Best J stated that he would refuse to recognise a statute legitimising slavery, since it would be "against the law of nature and God".
After this, the golden age of parliamentary supremacy set in, and the case-law overtly denying parliamentary supremacy dried up. In the 20th century, however, a series of Privy Council and Commonwealth cases confirmed that legislatures created within the British Empire could be bound as to the procedures that they had to follow in passing certain types of legislation (the cases were Attorney-General for New South Wales v Trethowan  AC 526, Harris v Dönges  1 TLR 1245 and Bribery Commissioner v Ranasinghe  AC 172). This principle is inconsistent with the traditional notion that no Parliament can bind its successors as to the "manner and form" of its legislation. While the issues at stake in those cases were distinguishable from those at stake in the British context, the cases are certainly not helpful to the cause of parliamentary supremacy.
In more recent years, one gets the impression that judges have gone rather cool on the traditional doctrine. The last ringing reaffirmation of parliamentary sovereignty in the highest court of the land came over a generation ago, in Pickin v British Railways Board  AC 765. Vice-Chancellor Megarry reaffirmed the doctrine in Manuel v Attorney General  Ch 77, but he expressly left out of account the consequences of membership of the EC. When Manuel reached the Court of Appeal, the appeal judges appeared to accept the traditional doctrine, but they curiously stopped short of affirming it in wholly clear, unequivocal terms. It may also be worth referring here to the case of Oppenheimer v Cattermole (1976) AC 249, in which Lord Cross said, in reference to an antisemitic Nazi law:
To my mind a law of this sort constitutes so grave an infringement of human rights that the courts of this country ought to refuse to recognise it as a law at all.Would the courts really never be prepared to come to a similar decision on a British statute?
The plates were definitely shifting by the 1990s. Lord Woolf stated in his F A Mann lecture in 1994:
If Parliament did the unthinkable then I would say that the courts would also be required to act in a manner which would be unprecedented.... I myself would consider there were advantages in making it clear that ultimately there are even limits on the supremacy of Parliament which it is the courts' inalienable responsibility to identify and uphold.Similar sentiments were expressed at around the same time by two other well-known judges, Sir John Laws and Sir Stephen Sedley. By this point, the doctrine of implied repeal - under which each Act of Parliament is taken as being the latest sovereign word of Parliament and hence as prevailing over all earlier legislation even where the latter is not expressly repealed - had passed into history with the House of Lords' decision in R v Secretary of State for Transport (ex parte Factortame) (No 2)  1 AC 603, a decision which was followed a few years later by Thoburn v Sunderland City Council  EWHC 195.
Most recently, parliamentary supremacy received a less than unqualified endorsement from the House of Lords in the Jackson v Attorney General litigation brought by the Countryside Alliance following the enactment of the Hunting Act 2004. Lord Steyn's speech in that case has already been mentioned. So has that of Lord Hope, who stopped short of an outright denial of the doctrine, but was nevertheless prepared to say:
...Parliamentary sovereignty is no longer, if it ever was, absolute.... It is no longer right to say that its freedom to legislate admits of no qualification whatever. Step by step, gradually but surely, the English principle of the absolute legislative sovereignty of Parliament which Dicey derived from Coke and Blackstone is being qualified.... The rule of law enforced by the courts is the ultimate controlling factor on which our constitution is based.Baroness Hale likewise said:
The courts will treat with particular suspicion (and might even reject) any attempt to subvert the rule of law by removing governmental action affecting the rights of the individual from all judicial scrutiny. Parliament has also, for the time being at least, limited its own powers by the European Communities Act 1972 and, in a different way, by the Human Rights Act 1998. It is possible that other qualifications may emerge in due course.Advocates of parliamentary sovereignty are, it seems, defending a doctrine that even the higher judiciary no longer fully believe in.
5. What about the EU?
In the popular media, the EU is frequently presented as the greatest contemporary menace to parliamentary sovereignty. In fact, however, it is a relatively minor threat. I have already discussed this point elsewhere. The courts of the EU consider that EU law prevails over the domestic constitutional arrangements of member states, but this doctrine is some distance from being accepted by the courts of the UK (and, indeed, by those of other member states, notably Germany).
Parliamentary supremacy has certainly been modified by the UK's membership of the EU. Most famously, the Factortame litigation resulted in the House of Lords taking the unprecedented step of granting an injunction to "disapply" an Act of Parliament, the Merchant Shipping Act 1988 ("disapply" is a neologism, from the Italian disapplicare - a new word had to be coined for what the Law Lords did). Nonetheless, EU law ultimately depends for its effect in the UK on an Act of Parliament, the European Communities Act 1972. This is emphasised in Section 18 of the recently enacted European Union Act 2011:
Directly applicable or directly effective EU law (that is, the rights, powers, liabilities, obligations, restrictions, remedies and procedures referred to in section 2(1) of the European Communities Act 1972) falls to be recognised and available in law in the United Kingdom only by virtue of that Act or where it is required to be recognised and available in law by virtue of any other Act.That sounds fairly clear. EU law applies in the UK because, and only because, Parliament says so. If we are looking for threats to parliamentary sovereignty, we would do better to look at Britain's own domestic legal tradition rather than at the European Union.