The aim of this paper is to analyse the long-term implications of leaving the EU for the UK economy. To do this, we consider three main channels by which the UK economy could be affected in the long run: 1) Reductions in trade with EU countries and a modest increase in tariff barriers.2) A reduction in foreign direct investment (FDI), particularly affecting services FDI.3) A reduction in the UK's net fiscal contribution to the EU.We input these effects of leaving the EU into NiGEM, the National Institute Global Econometric Model, a multicountry economic forecasting model. NiGEM has been developed at NIESR over the past three decades and is funded by subscriptions from international institutions, central banks and finance ministries from around the world, as well as some private sector institutions. Both the OECD and HM Treasury have also chosen to use NiGEM to conduct their analysis of the economic impact of leaving the EU. This is not surprising, as NiGEM's explicit trade linkages make it particularly well-suited to modelling the impact on the UK economy of shifts in trade policy.This article presents our estimates of the long-run impact of leaving the EU over the next fifteen years, not only on GDP, but on consumption, real wages, unemployment, and a range of other (endogenously determined) variables. We find that by 2030, GDP is projected to be between 1.5 per cent and 3.7 per cent lower than in the baseline forecast in which the UK remains in the EU. Real wages fall somewhat more, by between 2.2 per cent and 6.3 per cent. Consumption is also hit somewhat harder than GDP, falling by between 2.4 and 5.4 per cent. Real wages and consumption decline more than GDP in the long term due to a long-term deterioration in the terms of trade, coupled with a shift towards savings. Table 14 compares our estimated long-run reductions in GDP to those of three other prominent studies published by the OECD, the Centre for Economic Performance (CEP) at the LSE and HM Treasury. While the studies assume broadly similar reductions in trade and FDI, as well as similar reductions in the UK's net contributions to the EU, the range of estimated impacts on GDP relative to the 2030 baseline is considerably larger. We summarise these results by reporting the estimated reduction in GDP for each percentage point reduction in total trade. In the CEP analysis, GDP is reduced by 0.5 per cent to 0.75 per cent for each 1 per cent reduction in total trade, while in the OECD and HM Treasury studies, the reduction is about 0.3 per cent to 0.4 per cent of GDP for each 1 per cent decrease in total trade. In our analysis, GDP is reduced by 0.1 per cent for each 1 per cent reduction in trade, so that our estimates can be seen as more conservative.Our modelling strategy is to focus on a small number of the clearest and most well-understood potential impacts on the EU economy of leaving the EU in our core scenarios. As a result, it is not surprising that our estimated reductions in GDP are smaller than those of by guest on June 4, 2016 ner.sagepub.com D...