
Britain has an uncodified constitution. This means that it is constituted from a variety of sources, including: Statute Law, Common Law, Conventions, Royal Prerogative, External Relations and Works of Authority. Of these sources, many are uncodified, meaning they are not written down. This contrasts to a codified constitution like that of the United States in which the vast majority of constitutional rules are contained within the US Constitution which was signed in Philadelphia in 1787.
However, it is arguable that in recent years the British constitution has become increasingly codified as elements that were previously unwritten have been codified into Statute Law.
So, to what extent is it the case that the UK Constitution has been increasingly codified?
The increasing codification of conventions
Conventions are informal procedures that are commonly accepted as forming part of the constitution. As Britain’s constitution is uncodified and has developed organically, conventions have always played a significant constitutional role. However, in recent years there have been a number of conventions that have been codified into Statute Law:
Fixed-Term Parliaments Act (2011):

In Britain the government only holds power by virtue of the support of Parliament. Therefore, it was always a convention in the UK that it a government lost a motion of no confidence, it must resign and call a General Election. In 2011 the Coalition Government oversaw the passage of the Fixed-Term Parliaments Act (2011). This codified the circumstances in which an early general election should be called:
3) An early parliamentary general election is also to take place if—
Section 3 of the Fixed Term Parliaments Act (2011)
(a) the House of Commons passes a motion in the form set out in subsection (4), and
(b) the period of 14 days after the day on which that motion is passed ends without the House passing a motion in the form set out in subsection (5).
(4) The form of motion for the purposes of subsection (3)(a) is—
“That this House has no confidence in Her Majesty’s Government.”
(5) The form of motion for the purposes of subsection (3)(b) is—
“That this House has confidence in Her Majesty’s Government.”
Scotland Act (2016) and Wales Act (2017):

In 1998 Britain embarked upon a process of devolution with the Scotland Act, Wales Act and Government of Wales Act. These acts gave certain powers (devolved powers) to the nations of the UK but kept other powers (reserved powers) for the Westminster Parliament. However, because of parliamentary sovereignty, there was nothing to technically stop the Westminster Parliament from legislating on devolved issues. Therefore, a convention called the “Sewell Convention” (named after Lord Sewell) emerged that stipulated that the UK Parliament would “not normally legislate” on issues that were devolved without the consent of the devolved body (what is known as a legislative consent motion). Later, the Sewell Convention was codified into Statute Law in the Scotland Act (2016) and Wales Act (2017).
Posonby Rule:
The Posonby Rule was a convention that stipulated that any international treaty should be laid before Parliament at least 21 days before its ratification. By convention unless opposition parties notified the Government of concerns, there would be no debate and the treaty would come into law after 21 days.
However, under the Constitutional Reform and Governance Act (2010) put this requirement into Statute Law.
Key Constitutional Conventions that remain uncodified
Despite these codifications, a number of very important aspects of the UK constitution remain just conventions, including:
Salisbury Convention: This convention dictates that the House of Lords does not vote against a legislative motion that was part of the government’s election manifesto.
Financial Privilege of the House of Commons: This convention dictates that the House of Lords does not decide on tax and spending legislation.
The Prime Minister is the person who can best ‘command the confidence of the House of Commons’: This convention dictates that the Prime Minister is the person who can best ‘command the confidence of the House of Commons’. This person is normally the leader of the largest party in the House of Commons.

The Prime Minister must come from the House of Commons: Technically, the Prime Minister could govern from the House of Lords. However, convention now dictates that the Prime Minister holds a seat in the House of Commons.
The ‘somewhat’ increasing codification of Royal Prerogative Powers
Royal Prerogative powers are those that traditionally belonged to the monarch but are now exercised by the government (and often the Prime Minister). These powers make the Prime Minister extremely powerful and are often extremely difficult for Parliament to adequately scrutinize. However, like conventions, many Royal Prerogative powers have been codified in recent years and generally this has seen the government’s power diluted:
Fixed Term Parliaments Act (2011): Prior to the passing on the Fixed-Term Parliaments Act it up to the Prime Minister when to call a General Election, as long as it was there was no more than five years since the last. This gave the Prime Minister the ability to call a ‘snap election’ and choose an election timing that was to their own liking. However, since the Fixed Term Parliaments Act (2011) the date of the General Election next General Election is fixed in law. Under this Act, an early general election can only be held if:
- A motion of no confidence is held in a government.
- 2/3rds of Parliament vote for an early General Election.
On paper, this appeared to significantly reduce the power of the Prime Minister. However, it is worth noting that the Early Parliamentary General Election Act (2019) was passed to override the FTPA (2011) and hold the 2019 General Election.
There are other prerogative areas which remain that could be codified to allow more scrutiny of government. These include:
The Prime Ministers power to appoint their own Cabinet: Cabinet nominations could be made subject to a parliamentary vote, as they are in the United States.
The Prime Ministers power to launch military action: A ‘War Powers Act’ could be passed which limits the Prime Ministers power to order military action. This was muted by then Labour Leader Jeremy Corbyn following Theresa May’s decision to launch Air Strikes against Syria in 2018.
Importantly, for any of these to pass, it would likely require the approval of the governing party. It is unlikely for a Prime Minister to order his party to limit his or her own power.
In summary, in recent years there has been increasing codification of the UK constitution. However, fundamentally important aspects of the UK constitution remain uncodified. It is therefore not reasonable to say that Britain is heading towards a codified constitution from this.