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.
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.
[3] The next day the arrests were publicly queried in the House of Commons, and a Labour backbencher Jack Jones started a debate on the subject in the afternoon.
[3] A few days after the arrests the solicitors for one of the deported men, Art O'Brien, got in contact with Sir Patrick Hastings KC, a Member of Parliament for the Labour Party and a noted barrister.
[9] The court decided that the Restoration of Order in Ireland Act 1920 had been implicitly repealed when the Irish Free State, an independent nation, came into existence.