The United Kingdom and independence

For more than a century there has existed a debate about secession from what is now the United Kingdom of Great Britain and Northern Ireland. This began with Ireland in the early 20th century and continues today with Scotland and Wales.

This briefing looks at how the UK is currently constituted and the mechanisms by which a part of the UK could secede from it.

Legal basis of the United Kingdom

There is no founding document which established the “United Kingdom of Great Britain and Northern Ireland”. Rather, what political scientists describe as a multi-national state (or a State of Unions) has developed gradually over several centuries. According to the Cabinet Office, the United Kingdom “comprises four nations”.

England and Wales

Wales was annexed by the English Crown in 1284 under a prerogative act known as the Statute of Rhuddlan (or Statutes of Wales).

Under the Laws in Wales Act 1535, Wales was “incorporated with England” and granted representation in the Parliament of England. The Laws in Wales Act 1542 completed this incorporation.

Schedule 1 to the Interpretation Act 1978 defines “England” as the area consisting of the counties established under section 1 of the Local Government Act 1972, Greater London and the Isles of Scilly. “Wales” is defined as the combined area of the counties created under section 20 of the 1972 act, while section 158 of the Government of Wales Act 2006 defines “Wales” as including the “sea adjacent to Wales out as far as the seaward boundary of the territorial sea”. “English border area”, meanwhile, means “a part of England adjoining Wales (but not the whole of England)”.

Paragraph 5 of schedule 2 to the Interpretation Act 1978 provides that in any act passed before 1 April 1974, a reference to England includes Berwick-upon-Tweed and Monmouthshire and, in the case of an act passed before the Welsh Language Act 1967, Wales.

England and Scotland

Following the 1603 Union of the Crowns, England (which was taken to include Wales) and Scotland remained separate kingdoms, but shared a monarch. This was a “personal union” of crowns, with different laws of succession in Scotland and in England. A fuller “incorporating” (rather than federal) union followed in 1707.

Article I of the 1706 Treaty of Union (signed at Westminster on 22 July) stated that the kingdoms of Scotland and England would on 1 May 1707 “and for ever after, be united into one Kingdom by the name of Great-Britain”; Article III that it “be represented by one and the same Parliament, to be st[y]led the Parliament of Great-Britain”. The treaty required ratification and legislation in both parliaments. The Union with England Act 1707 was passed by the Parliament of Scotland and the Union with Scotland Act 1706 by the Parliament of England. These are often referred to collectively as the “Acts of Union 1707”.

In October 1707, the Scottish and English parliaments were replaced by a single “Parliament of Great Britain” (which included 45 Scottish MPs and 16 “representative” peers). The Parliament of Great Britain subsequently passed the Union with Scotland (Amendment) Act 1707, which replaced the Privy Councils of England and Scotland with a new Privy Council of Great Britain. There remained a separate Privy Council for Ireland.

Some Scottish lawyers have argued that (in Scots, if not English, law) this union legislation enjoyed a special status which made it unalterable by the GB/UK Parliament. Nevertheless, 14 Articles of the Union were repealed wholly or in part by the Statute Law Revision Acts of 1867, 1871, 1906 and 1948. Scotland’s representation in the Commons was also increased via legislation, while the Peerage Act 1963 scrapped the system of representative peers introduced in 1707.

The territory of Scotland (and therefore of the UK) was expanded to include Rockall in 1956, initially under the royal prerogative, and subsequently via statute. Section 126 of the Scotland Act 1998 defines “Scotland” as including “so much of the internal waters and territorial sea of the United Kingdom as are adjacent to Scotland”.

Great Britain and Ireland

The Crown of Ireland Act 1542 (enacted by the Parliament of Ireland) created the title of "King of Ireland" for King Henry VIII of England and his successors. The (British) Union with Ireland Act 1800 and (Irish) Act of Union (Ireland) 1800 abolished the Parliament of Ireland and declared that “for ever after” the Kingdoms of Great Britain and Ireland would “be united into one Kingdom, by the name of the United Kingdom of Great Britain and Ireland”. Its single Parliament included 100 Irish MPs and 28 representative peers.

Following a long campaign for “Home Rule” (or devolution) for Ireland, the Government of Ireland Act 1920 partitioned Ireland and created a devolved Parliament of Southern Ireland and a devolved Parliament of Northern Ireland. For the purposes of that act, Northern Ireland was defined as the:

parliamentary counties of Antrim, Armagh, Down, Fermanagh, Londonderry and Tyrone, and the parliamentary boroughs of Belfast and Londonderry.

While Southern Ireland was defined as consisting:

of so much of Ireland as is not comprised within the said parliamentary counties and boroughs.

The 1921 Anglo-Irish Treaty acknowledged Southern Ireland’s wish to secede from the UK. This was ratified by the Irish Free State (Agreement) Act 1922 and the Irish Free State (Consequential Provisions) Act 1922. Under the Irish Free State Constitution Act 1922 the “Irish Free State” was proclaimed by King George V on 6 December 1922. The Ireland Act 1949 recognised what later became the Republic of Ireland’s departure from the British Commonwealth of Nations. Section 46 of the Interpretation Act (Northern Ireland) 1954 defines “Republic of Ireland” as the territory which, in accordance with the provisions of the two 1922 acts, “was required to be styled and known as the Irish Free State”.

Section 6 of the Irish Free State (Consequential Provisions) Act 1922 provided for the King in Council to adapt enactments “as a consequence of the establishment of the Irish Free State”. The Irish Free State (Consequential Adaptation of Enactments) Order, 1923 provided that:

references in any enactment passed before the establishment of the Irish Free State to “the United Kingdom” or “the United Kingdom of Great Britain and Ireland,” […] shall, in the application of the enactment to any part of Great Britain and Ireland other than the Irish Free State, be construed as exclusive of the Irish Free State.

Great Britain and Northern Ireland

The Anglo-Irish Treaty and ratifying legislation enabled the devolved Parliament of Northern Ireland to determine its own constitutional future.

On 7 December 1922, the House of Commons and Senate of Northern Ireland resolved to remain a devolved part of the UK rather than form an autonomous part of the Irish Free State. This established a precedent for what later became known as the “principle of consent”.

The boundary between Northern Ireland and the Irish Free State was settled via amendment of the Anglo-Irish Treaty in December 1925. The UK Parliament passed the Ireland (Confirmation of Agreement) Act 1925 while the Free State passed the corresponding Treaty (Confirmation of Amending Agreement) Act, 1925.

At the instigation of the Irish Free State, the UK Parliament also passed the Royal and Parliamentary Titles Act 1927. This changed the name of the “Parliament of the United Kingdom of Great Britain and Ireland” to the “Parliament of the United Kingdom of Great Britain and Northern Ireland”. Schedule 1 to the Interpretation Act 1978 thus defines “United Kingdom” as meaning “Great Britain and Northern Ireland”. Section 2(2) of the 1927 act also provided that in every public document issued after the passing of that act the expression “United Kingdom” meant “unless the context otherwise requires […] Great Britain and Northern Ireland”.

The bicameral Parliament of Northern Ireland was prorogued under section 1(3) of the Northern Ireland (Temporary Provisions) Act 1972 and abolished under section 31(1) of the Northern Ireland Constitution Act 1973. Section 42 of the 1973 act included a saving provision that abolition did not “affect the validity or otherwise of any Act of that Parliament”.

Leaving the Union(s)

The United Kingdom has been described by the Welsh Government as a “voluntary union of 4 nations” – England, Scotland, Northern Ireland and Wales – “which come together to share resources and risks”.

The “Union of the Kingdoms of Scotland and England” is a reserved matter under schedule 5 to the Scotland Act 1998, as is “the union of the nations of Wales and England” under schedule 7A to the Government of Wales Act 2006. The union of Great Britain and Northern Ireland is not an excepted or reserved matter under the Northern Ireland Act 1998.

Northern Ireland

Section 1(1) of the Northern Ireland 1998 Act provides that Northern Ireland:

in its entirety remains part of the United Kingdom and shall not cease to be so without the consent of a majority of the people of Northern Ireland voting in a poll held for the purposes of this section in accordance with Schedule 1.

Under schedule 1 to the 1998 act, the Secretary of State for Northern Ireland may “direct the holding of a poll for the purposes of section 1” on a date specified in an order, while he or she “shall” (or must) exercise the same power:

if at any time it appears likely to him that a majority of those voting would express a wish that Northern Ireland should cease to be part of the United Kingdom and form part of a united Ireland.

Attempts in the courts to clarify the “mechanism” for directing what is often called a “border poll” have failed. The Northern Ireland Court of Appeal found this would “contravene the constitutional value of flexibility”. If a majority (in Northern Ireland) were to endorse Irish unification in such a poll, then the Secretary of State must:

lay before Parliament such proposals to give effect to that wish as may be agreed between [His] Majesty’s Government in the United Kingdom and the Government of Ireland.

If a referendum is held and does not endorse unification, then another border poll cannot be held for seven years.

Case law has consistently established that this “principle of consent” relates only to Northern Ireland’s status (PDF) as part (or not) of the United Kingdom, not to other changes regarding its governing arrangements.

In February 2024, the House of Commons passed an Address to the King which reaffirmed the constitutional status of Northern Ireland. Since the 1993 Downing Street Declaration, the UK Government has maintained that it has “no selfish strategic or economic interest in Northern Ireland”.

Scotland and Wales

No equivalent provision exists for Scotland or Wales to determine their constitutional status.

Scotland

Under the non-statutory Edinburgh Agreement of 2012, the Scottish and UK governments agreed to facilitate an Order in Council under section 30 of the Scotland Act 1998 to allow a single-question referendum on Scottish independence to be held before the end of 2014. The Scottish Government then introduced legislation in the Scottish Parliament to that end. No further action was necessary when the people of Scotland voted by 55% to 45% to remain part of the United Kingdom. In the event of a “yes” vote, the Scottish Government intended that a Scottish Independence Act 2015 (an Act of the Scottish Parliament) would have provided for an “interim constitution” pending a permanent codified constitution agreed “by or on behalf of the people of Scotland”.

In 2022, the United Kingdom Supreme Court ruled that the Scottish Parliament did not have the unilateral “power to legislate for a referendum on Scottish independence”, although the earlier Smith Commission report observed that nothing in that report (proposals for further devolution) prevented Scotland “becoming an independent country in the future should the people of Scotland so choose”.

Wales

In 2021, the Labour-led Welsh Government expressed the view that, provided a devolved government in either Scotland or Wales had:

secured an explicit electoral mandate for the holding of a referendum [on independence], and enjoys continuing support from its parliament to do so, it is entitled to expect the UK Parliament to take whatever action is necessary to ensure that the appropriate arrangements can be made.

Plaid Cymru and SNP policy

Ahead of the devolved elections in 2026, Plaid Cymru (the largest pro-independence party in Wales) and the Scottish National Party (the largest pro-independence party in Scotland) both said they would pursue the powers required to hold independence referendums.

Plaid Cymru

In Plaid Cymru’s manifesto for the 2026 Senedd elections, the party said:

We fundamentally believe that the decision on Wales’s political and constitutional future belongs to the people of Wales. We will therefore formally request that the right to decide on the timeline, question and process for an independence referendum be devolved.

This would require an amendment to the Government of Wales Act 2006. Section 58A and section 109 provide for transfers of executive and legislative functions between the UK and Welsh parliaments. The latter (Section 109 Orders) require approval from both the UK Parliament and the Senedd.

Plaid has also pledged to establish a new National Commission for Wales, which will:

• engage citizens “in an ongoing national conversation about the options for Wales’s constitutional future”
• research “key political and economic questions relevant to Wales’s constitutional future”
• lay the “foundations” for a future white paper on Welsh independence

Plaid leader Rhun ap Iorwerth said at his party's annual conference in October 2025 that:

it is us that should call the referendum when the time is right. But that's not for now or the next government. Our work now is to take the discussion forward on the next steps for Wales's constitutional journey.

Scottish National Party

In its manifesto for the 2026 Scottish Parliament elections, the Scottish National Party said that:

The only time Westminster has ever respected Scotland’s right to decide was when, at the 2011 election, the people of Scotland delivered a majority of SNP MSPs [Members of the Scottish Parliament]. A vote for the SNP is a vote for a referendum on independence. Based on the 2011 precedent, an SNP majority at this election is a mandate for the transfer of powers to the Scottish Parliament to enable an independence referendum to be held.

The SNP did not win an overall majority at the election on 7 May 2026.

At the 2025 SNP conference last year, the First Minister of Scotland, John Swinney, said he would deploy undisclosed “tactics” to secure another independence referendum, should the UK Government refuse to grant a Section 30 Order (see above). One delegate suggested the Scottish Government could judicially review a refusal, although several constitutional experts told the Scottish Parliament’s Constitution, Europe, External Affairs and Culture Committee that the 2011 precedent would not be considered legally binding by the courts.

Separately, John Swinney has pledged to:

• publish a draft Scottish Referendum Bill
• convene a constitutional convention to help inform this legislation
• bring forward a Holyrood vote to approve the development of a Section 30 Order on the first sitting day after the appointment of the new Scottish Government