Inner circle cross-variational studies of tag questions (TQs) with interrogative tags (e.g. is it?, will they?) have focused exclusively on contrasting TQs in British and American English to date (cf., e.g., Algeo 1990; Allerton 2009; Roesle 2001; Tottie and Hoffmann 2006). Also, studies of tag questions in Irish English are primarily restricted to the level of form, analyses having focused on syntactic features in isolation without any regard to the functional level (cf. e.g. Hickey 2007, 2008; Lucek 2011; Kallen and Kirk 2012). The present paper meets these gaps by contrasting TQ use in Ireland and Great Britain on a formal and functional level using spoken data from the Irish and British components of the International Corpus of English. The analysis is based on a part corpus-based, part corpus-driven functional categorisation. Findings reveal many similarities across cultures but also point to a significantly lower use of TQs in Irish English. In addition, a higher use of TQs realising a question function and a lower use of TQs used to make statements is recorded in ICE-Ireland relative to ICE-GB, a situation which is suggested to have historical roots. On a formal level, use of positive constant polarity TQs was significantly higher in the Irish data, as was the use of the interrogative mood. Form-function correlations are also reported.