My Department's Budget 2017 macroeconomic forecasts incorporate a number of factors including the impact of budgetary measures at a macro level. The macro-drivers are then applied to tax revenue base and assist along with other factors in the production of the tax revenue forecasts.
Budgetary decisions are made factoring in all available data, including cross-border considerations. Excise rates are only one variable price component of cross-border trade. The applicable VAT rate in both jurisdictions is another variable and Sterling and Euro exchange rate provides the largest variable.
The Revenue carry out regular cross-border survey's which chart price differentials using a representative sample across all excisable products. This information is published on the Revenue website.