Since the onset of the global financial crisis in 2008 and the development of austerity as a widespread economic strategy there has been continuing focus on the tax gap as an issue, which is the difference between the amount of tax that should, theoretically, be collected by a tax authority within the prevailing system that a tax jurisdiction has legislated for and the actual amount of tax collected. The efficiency, or otherwise, of a tax authority in tackling the tax gap has come to be seen as a measure of its effectiveness in raising revenue, whether to balance budgets or fund additional government spending. Despite this, relatively little formal attention has been given to technical dimensions of the tax gap, or to the link between that tax gap and tax authority spending. We have sought to address these last issues. In the process we have appraised the quality of the data available for this process, including whether available GDP data is reliable as a basis for estimation; whether data on tax collected is comparable and whether available data on tax authority spending is appropriate for this purpose. Data on estimates of the shadow economy have also been appraised as a consequence. Whilst it has proved possible to prepare new estimates of the tax gap for EU member states limitations in the resulting estimates are highlighted. In addition, weaknesses in all other data sources are noted, and their suitability is questioned. The resulting analysis of tax authority expenditure and its relationship to the tax gap is, consequently, heavily constrained, but in any event no apparent statistical association is noted. It is suggested that other approaches to the 2 management of the tax, and the effectiveness of tax authorities, are required, with a recommendation that tax spillover assessments be considered as an alternative
