The UK does not have a codified constitution and constitutional matters are not among the powers devolved to Scotland, Wales or Northern Ireland. Under the doctrine of parliamentary sovereignty, the UK Parliament could, in theory, therefore, abolish the Scottish Parliament, Senedd or Northern Ireland Assembly. Indeed, in 1972, the UK Parliament unilaterally prorogued the Parliament of Northern Ireland, setting a precedent relevant to contemporary devolved institutions. In practice, it would be politically difficult for the UK Parliament to abolish devolution to the Scottish Parliament and the Senedd, given the political entrenchment created by referendum decisions. The political constraints placed upon the UK Parliament's power to interfere with devolution in Northern Ireland are even greater than in relation to Scotland and Wales, given that devolution in Northern Ireland rests upon an international agreement with the Government of Ireland.