By Alison L Young
Sir David Williams Professor of Public Law, University of Cambridge

Sometimes, when political debates get heated, actions are criticised for being ‘unconstitutional’. Was it unconstitutional for backbench and opposition MPs to make an Act of Parliament to stop the UK leaving the EU without a deal? Or for the Prime Minister to prorogue (suspend) Parliament for five weeks? Or for Parliament to make an Act of Parliament that would give the Government the power to act contrary to international law?

Yet, we’re also told that the UK does not have a codified Constitution. You cannot go to a library or book shop and pick up a copy of the UK constitution, like you could, for example, in the US or Germany. When a law is unconstitutional in the US, it means that the law is quashed. So, in the US, when the US Supreme Court ruled that laws restricting same-sex marriage were unlawful, it meant laws that prevented same-sex marriage were unlawful. They could not be enforced. And new laws could not be made to prevent same-sex marriage.

The same is not true in the UK. We do have laws enabling same-sex marriage. But it would be possible for laws to be passed in the future to make same-sex marriage unlawful. The UK does not have a constitution that would prevent the UK from making laws. This is because the UK’s Westminster Parliament is sovereign. The Human Rights Act 1998 does protect human rights. So, if a law was passed that restricted same-sex marriage, the court would, if possible, be able to read this law to protect same-sex marriage.

But what would happen if a new law overturned same-sex marriage, making it unlawful? There is nothing the UK courts could do, other than declare the law to be a breach of human rights – a declaration of incompatibility. Any declaration of incompatibility would not stop the restriction on same-sex marriage from being a valid law that could be enforced by the courts.

It would be possible to go to the European Court of Human Rights in Strasbourg. This is an international court which protects the rights found in the European Convention of Human Rights (ECHR). If it decided the UK’s new law preventing same-sex marriage breached the ECHR, then this would mean that the UK was in breach of its obligations in international law. This would not mean that the law would change in the UK. But it would put pressure on the UK to change its law in order to protect rights.

So does this mean the UK does not have a constitution?

Even though the UK does not have a codified constitution, it does have lots of rules that regulate what we call constitutional issues. There are rules that set out the powers of governmental institutions, that explain the relationship between them, and that protect human rights.

These rules can be found in lots of different places. We have Acts of Parliament that regulate constitutional issues. The Human Rights Act 1998, for example, protects human rights found in the ECHR. There is also legislation regulating how we vote in general elections, and setting up governments and law-making institutions in Scotland, Wales and Northern Ireland.

Acts of Parliament are the highest form of law in the land. But some Acts of Parliament are more important than others. Legislation that regulates constitutional matters is more important. It’s harder for Parliament to change constitutional statutes. Most legislation can be changed merely by Parliament enacting a new law that changes the old law. Constitutional statutes are different. Parliament has to state clearly that it is overturning a constitutional statute.

We find rules regulating constitutional issues in other places too. Acts of Parliament can give the government the power to make regulations. We call this delegated legislation. Delegated legislation was used to regulate Covid lockdowns. Immigration is also controlled through delegated legislation.

Acts of Parliament are more important than regulations. Regulations cannot contradict Acts of Parliament. Courts can also review regulations. If a regulation contradicts an Act of Parliament, then a court can quash the regulation. The same is true if a regulation contradicts human rights protected under the Human Rights Act 1998.

The constitution is also regulated by the common law. The common law is found in decisions of the courts. When courts look at acts of the government, to check if they are unlawful, they apply principles of judicial review. These principles come from the common law. If a decision of the government was made when the government did not have the power to act, or if it took a decision without following the right procedures, or a decision that was irrational, the courts can quash the government’s decision as unlawful.

Some governmental powers come from the common law and not from Acts of Parliament. These are called prerogative powers. When the government uses a prerogative power, the courts can check whether the government has gone beyond the scope of its powers. Courts can also review how most – but not all – prerogative powers are used. Some important aspects of the constitution are found in prerogative powers; for example, the power to prorogue (suspend) Parliament, to deploy troops, or to enter into Treaties with other countries.

Some aspects of the constitution, however, are not regulated by Acts of Parliament, regulations, prerogatives or the common law. One type of rule is a conventions. Conventions are rules that stem from practice.  For example, conventions regulate how often the Westminster Parliament holds Prime Ministerial questions. By convention, the Government only remains in power when it has the confidence of the House of Commons – when the majority of MPs would vote in favour of the Government’s decisions. Acts of Parliament are made by the House of Commons, the House of Lords and the Monarch. By convention, the Monarch gives consent to Acts of Parliament – unless her Government advises the Monarch not to.

Conventions are not created by the courts and cannot be enforced by the courts. So, how are they enforced? There are normally political consequences for breaching a convention. If the Government tried to continue in power when it did not have the confidence of the House of Commons, it would find it difficult to do its job. All of the law it tried to make would not be voted for by a majority of MPs.

There are also other rules that regulate how Parliament works. Some of these are called Standing Orders. For example, Standing Order number 14 prioritises the business of the Government in the House of Commons.

So when is something unconstitutional?

Sometimes the rules tell is when something is unconstitutional. Was it unconstitutional for Parliament to pass legislation to stop the UK leaving the EU without a deal? Not according to the Standing Orders. The Speaker is in charge of determining what the Standing Orders mean. He decided that the Standing Orders did allow Parliament to debate, vote for, and make that law.

What about the suspension of Parliament? The Supreme Court decided that it was unlawful for the Prime Minister to advise the Monarch to prorogue Parliament for five weeks without a reasonable justification. The court quashed the prorogation order, meaning that Parliament was able to return to work.

What about an Act of Parliament empowering the Government to act contrary to international law? Because of parliamentary sovereignty, Parliament can give this power to the Government. It would not be unlawful. But would that mean it was constitutional?

It’s not easy to work out whether something is unconstitutional in the UK. Things can be unlawful, but some would argue that they are still not unconstitutional. And things can be lawful, but some would argue that they are still unconstitutional. How can that be? Often, when we say that something is unconstitutional, we mean that we think it is not the right thing to do according to how we think the constitution should work — but that might not be the same as what it right (lawful) according to the law.