Double Taxation Relief Manual: Guidance by country: Ireland: Capital gains
A resident of Ireland is chargeable to United Kingdom Capital Gains Tax if
a) he is also resident or ordinarily resident in the United Kingdom on gains accruing to him from the disposal of immovable property situated in the United Kingdom or in Ireland, or of unquoted shares deriving their value from such property. Where the immovable property is situated in Ireland, credit will be due for the Irish Capital Gains Tax against the United Kingdom tax on the same gain; or
b) he is also resident or ordinarily resident in the United Kingdom and provided he is not domiciled in Ireland, on gains accruing to him from the disposal of assets outside both countries if the gains are not remitted to Ireland. The assessment in this case is to be made on the remittance basis if the taxpayer is domiciled in a third country;
c) he is trading in the United Kingdom through a branch or agency (see DT9886).