The @UKandEU programme has attempted to model the economic impact of Boris Johnson's Brexit Deal. As the authors of the report acknowledge, economic modelling is not an exact science, but the results make grim reading. Some highlights follow. ukandeu.ac.uk/wp-content/upl…
@UKandEU 1. Changes to trade: "Relative to staying in the EU, income per capita in the UK would be 2.5% lower under Mr Johnson’s proposals, compared to 1.7% under Mrs May’s deal". "The decline in income per capita under Mr Johnson’s proposals is 50% greater than for Mrs May’s deal". 
@UKandEU 2. Include the effects of trade on productivity, and the costs are even greater. "Under Mr Johnson’s proposals, income per capita falls by 6.4%, whereas under Mrs May’s deal it falls by 4.9%".
@UKandEU 3. On public spending: "Our most optimistic scenario suggests that ... Mr Johnson’s deal would leave the public finances £16 billion worse off". "Our most pessimistic scenario forecasts a much greater impact on the public purse, of around £49 billion". (Defence Spending is £39b).
@UKandEU 4. To sum up: "the economic impacts of Mr Johnson’s proposals are substantially negative ... Our most optimistic scenario—assuming no productivity effect and a relatively liberal approach to migration—suggests that income per capita would by 2.3% lower in the long term".
@UKandEU 5. Economic predictions are fraught with peril, and the costs of leaving with No Deal would be even higher. But there is no rational case for doubting that, over time, Boris Johnson's deal would deliver a significant hit to the UK economy. MPs should study this report with care.
@UKandEU Postscript: it is true to say that Brexit will be only one variable in Britain's future economic performance. Others might include global economic shocks, US-China relations, climate change, fiscal policy & more. So we can't say with any certainty "in 2030, GDP will be X". BUT...
@UKandEU ... we *can* & should assess the likely impact of changes that we *choose* to make, & whether their tendency is to make trade harder or easier, to create jobs or destroy them. Sticking our fingers in our ears & urging sceptics to "believe in Brexit" is not a responsible policy.
