I think you would be able to claim simultaneous PPRs in each jurusdiction, providing you were occupying both, and automatically extended into the post-occupation exemption period. However, the tax inspector might demand justification if you were not registered as a taxpayer in the relevant jurisdiction. However, under the double taxation treaty a person could seem to be qualified by mere residence to be tax-resident in both simultaneously, in which case 'tax residence' is decided by which jurisdiction is dominant in your affairs. So you could have a PPR in both countries although tax-resident in only one. I do not think either the UK or Irish tax authorities will query your UK PPR. Your problem will be to convince the Irish authorities that you had a PPR in Ireland, although never a tax payer.