Though the counties that constituted Northern Ireland opted out of the Irish Free State in 1921, it was another 8 years before they reverted back to the single-seat constituency system used by the rest of the UK. Used for just one further election in 1925, these constituencies operated on proportional representation and remained unchanged for their entire tenure. The numbers weighed in the favour of the unionist population: predominantly nationalist counties Fermanagh and Tyrone were merged with a shared total of 8 seats. This bias showed itself strongly in election results, with the UUP winning huge majorities both times.
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