R v Secretary of State for Home Affairs, ex p O'Brien

R v Secretary of State for Home Affairs ex parte O'Brien [1923] 2 KB 361 was a 1923 test case in English law that sought to have the internment and deportation of Irish nationalist sympathisers earlier that year declared legally invalid. In March 1923 between 80 and 100 suspected Irish nationalists in Britain were arrested by the police and sent to the Irish Free State under the Restoration of Order in Ireland Act 1920 (ROIA). One of the detainees, Art O'Brien, challenged his detention in a test case at a divisional court. The case eventually went to both the Court of Appeal and House of Lords, who decided that the internments were illegal because the Irish Free State was an independent nation and so British acts of Parliament no longer applied to it.

The decision effectively illegalised the ROIA and led to the immediate release of O'Brien and the other detained individuals, who sued the British Government for false imprisonment. The government pushed through the Restoration of Order in Ireland (Indemnity) Act 1923, which limited the money they had to pay the detainees, who eventually received £43,000. O'Brien himself was re-arrested and found guilty of sedition, and was imprisoned until 1924.