You wait for months for an analysis of the economic impacts of Brexit, and then three come along at once. But, in contrast to the public perception that economists can’t agree on even the most basic questions, like whether austerity was necessary or desirable, what is most striking about the reports published this week is how much they have in common. All three analyses this week (a report funded by the People’s Vote and produced by National Institute of Economic and Social Research (NIESR); the UK in a Changing Europe report that I and Thomas Sampson of LSE co-wrote; and, most importantly, today’s “cross-government long-term economic analysis”) all share the same basic messages.

We all agree that both the theoretical and empirical evidence show that making the UK less open to trade and migration will reduce the size of the UK economy, compared with remaining in the EU, so Brexit will, over the long run, make us somewhat poorer than we would otherwise be. We all agree that a no-deal Brexit will – even leaving aside the short-term disruption that would inevitably result – have by far the largest negative impact. And we are not that far apart on the likely impact of the actual Brexit deal on the table, although that message has somewhat been obscured by the political spin.

We should give real credit to economists within government for producing a thorough and professional analysis, under both time constraints and, no doubt, considerable political pressure.

Somewhat unfortunately, the government paper does include a scenario described as “modelled white paper” – that is, the Chequers deal – and government ministers have chosen to focus on this, relatively benign, outcome. But this is, of course, pure fantasy. What Chequers means in terms of the assumptions the government has fed into its economic model is “frictionless trade” – a phrase that, despite Theresa May’s best efforts, appears nowhere in the withdrawal agreement or political declaration on the UK’s future trading relationship with the EU.

The government has also, commendably, modelled a much more realistic scenario, under which Brexit results in a significant increase in non-tariff barriers, but not by as much as would occur if we simply moved to a “Canada-style” free trade agreement, still less a no-deal scenario. This is a much more plausible representation of what the deal the government has actually signed will mean in practice. And it is these new barriers to trade that are the main driver of the economic impacts.

But there are also other factors. The government modelling also looks at the impact of reduced immigration from the EU after free movement ends, and finds that this will have a further negative impact – not just on total GDP, but also on GDP per capita and hence average incomes. As it says, we don’t yet know what immigration policy will look like after Brexit – the long-promised white paper is due out shortly – but it’s interesting that even the government admits that Theresa May’s objective of sharp reductions in EU migration will make us considerably poorer.

And the government analysis also factors in trade deals – not just with the US, but with countries from Australia to Brunei to China. Frankly, given that the deal on the table is likely to keep us in a customs union with the EU for the indefinite future, this is pie in the sky (as Donald Trump correctly pointed out) but it hardly changes the numbers. Even under the government’s optimistic assumptions, trade deals with third countries simply don’t boost growth by very much – only 0.1% of GDP.

So what’s the bottom line? Looking at their realistic scenario rather than the Chequers fantasy, the cross-government analysis suggests that the Brexit deal would reduce UK GDP by between 2% and 4% (and that GDP per capita would fall by between 2% and 3%). Our report estimated a hit to GDP per capita of between 1.9% and 5.5%. Given the uncertainties involved, these results are reasonably consistent.

And what about the public finances? Well, there’s certainly not going to be any extra money for the NHS, or anything else. The government estimates that the cost to the public finances would be up to £24bn. You could fill that gap by increasing VAT by four percentage points – or alternatively by cancelling the entirety of the government’s planned increase in health spending.

The bottom line? There were claims today that this analysis shows that the “deal on the table is the best deal”. It does show that this deal – indeed, any deal – is considerably better than no deal. But, consistent with all credible independent forecasts, it also shows that the “deal on the table” will, over time, make us considerably poorer than we would otherwise have been.

• Jonathan Portes is a senior fellow of the UK in a Changing Europe programme. This piece was co-authored with Thomas Sampson, assistant professor of economics at the London School of Economics