UK could actually split? Experts explain the legal route facing independence leaders

Agreements make political claims

SNP leader and Scottish First Minister John Swinney, Plaid Cymru leader Rhun ap Iorwerth, and Sinn Féin leaders Michelle O’Neill and Mary Lou McDonald signed a memorandum of understanding. The meeting was held among party leaders, not first ministers, though O’Neill was criticised by Northern Ireland unionists for attending while serving as first minister.

Swinney and ap Iorwerth also signed the Cardiff Agreement for their governments. It describes the UK as unjust and unsustainable and calls for greater devolved powers over constitutional matters, but does not alter either government’s legal authority.

Self-determination and the law

The memorandum asserts that the three nations have a right to self-determination and that Westminster should not block democracy. The governments’ agreement uses narrower language, referring to citizens deciding their constitutional future through democratic means.

International law does not generally give part of a state an automatic right to secede, except possibly in cases such as colonial rule or extreme oppression. The UK Supreme Court’s 2022 ruling, drawing on a Canadian Supreme Court decision on Quebec, likewise treated claims that Westminster cannot block a choice as political arguments, not statements of law.

Northern Ireland’s treaty-backed route

Reunification also requires a majority in the Republic of Ireland, reflecting a requirement in the Irish constitution. The votes do not have to take place on the same day, but both are needed.

Scotland and Wales face barriers

Scotland needs a section 30 order to hold an independence referendum, as it did before the 2014 vote. Successive prime ministers have refused to transfer that power, and the Scottish government’s draft referendum bill, published in August, cannot be introduced without the order.