Along with the Rule of Law, AV Dicey called Parliamentary Sovereignty one of the ‘Twin Pillars of the the UK Constitution’. Parliamentary Sovereignty is the most important principle of the UK constitution – although its [meaning] has been increasingly questioned in recent years.

Sovereignty means ultimate power. Parliamentary Sovereignty means that in the United Kingdom’s representative political system, Parliament has the ultimate power.

AV Dicey summed up Parliamentary Sovereignty simply by saying that Parliament could “make or unmake any law”. However, he also fully explained that there were three key facets to the principle:

1. Parliament can make laws concerning any matter

Parliament can legislate on any issue it chooses. In his book The British Constitution Anthony King said that Parliament could pass a law that banned smoking on the streets of Paris. Of course, this law would have no practical effect, but this would not stop Parliament from passing it. The fact that Parliament can make any law enforces its sovereignty. Any Statute Law passed by Parliament supersedes Common Law.

2. No Parliament can bind its successor

Each individual Parliament is sovereign. This means that no Parliament can pass a law that could not later be repealed by a future Parliament. As part of this a principle there also exists a doctrine of ‘implied repeal’. This means that if an Act of Parliament conflicts with an earlier act, the later Act automatically takes precedence, in effect repealing the earlier Act.

The best current example of Parliament not being able to bind its successor can be seen through Brexit. In 1972 Parliament passed the European Communities Act. This act saw Britain join the EEC (now EU). However, in June 2018 the EU (Withdrawal) Act was passed by Parliament following the result of the EU Referendum. This is the piece of law that will formally see Britain leave the European Union. This clearly shows that Parliament can repeal any Act by its predecessors.

3.  A valid Act of Parliament cannot be overturned by any other body 

As a result of Parliament’s Sovereignty, no Act or decision it takes can be overturned by another body, such as a court. This is fundamentally different from the United States. As the US has as Codified Constitution all actions that Congress takes must be in line with the Constitution. The courts can strike-down any action which is not in line with the Constitution. As Britain has no codified constitution, the courts cannot do this. Although the courts may advise Parliament on an issue, there is no mechanism for the striking down of a Parliamentary action.

These are the principles that underpin Parliamentary Sovereignty. These principles are all examples of legal sovereignty, the situation that exists in established law. However, this is different from political sovereignty, the situation that exists in practice.

There are a number of factors that potentially challenge the traditional principle of Parliamentary Sovereignty in the UK:

External Law – Britain has a number of external commitments that affect the ability of Parliament to remain sovereign. For example, Britain is a member of NATO. As part of this, Britain has made a guarantee to go to war to protect any other NATO member who is attacked.

The most prominent way that parliamentary sovereignty has been argued to be externally limited is because of Britain’s membership of the EU. When Britain joined the EU (then EEC) in 1972 they agreed to accept the precedence of EU Law over UK Law. This was later confirmed by the Factortame Case of 1990.

As Britain is due to leave the EU in March 2019 through the European (Withdrawal) Act, it is clear that legal sovereignty has never been lost. However, the reality is that as a member of the EU Parliament is not truly sovereign.

Devolution – It has been argued that Devolution has reduced Parliamentary Sovereignty. Although Devolution could be legally reversed it is now a deeply engrained part of the British political system. Since the first acts of devolution in 1998 the number of devolved powers has continued to grow. Technically the UK Parliament could pass legislation on ‘devolved powers’. For example, the UK Parliament could pass a law that said that Scottish students should pay the same tuition fees as English students. However, in reality, they would never do this as it would create a constitutional crisis – clearly showing Parliament’s sovereignty has been reduced.

Growing Judicial Activism – The British judiciary is seen to be increasingly independent

and, with this independence, more of an authority. The passing of the Constitutional Reform Act (2005) saw both the creation of the UK Supreme Court and the creation of the Judicial Appointments Commission. The UK Supreme Court’s role in Judicial Review has grown and a number of decisions against the Executive have occurred. One example is Evans v. Attorney-General in which the Supreme Court ruled that Prince Charles’ letters to Government Ministers should be released under the Freedom of Information Act (2000). However, by far the most prominent case is Miller v. Secretary of State for Exiting the European Union. In this case the Supreme Court said that it was not within the powers of the Royal Prerogative for the Government to initiate Article 50 and instead this power belonged to Parliament. This case actual reinforced Parliamentary Sovereignty but did so by accentuating the power of the Judiciary.

Elective Dictatorship – The domination of Parliament by the Executive, what Lord Hailsham called the ‘Elective Dictatorship’, might also be seen to limited Parliamentary Sovereignty. The Government usually as an in-built majority in the House of Commons and control the legislative agenda. As a result of this, they can largely push through whatever actions they believe to be necessary. Arguably, this means that sovereignty resides with the Government and not the wider Parliament.