We should assume that today’s OECD report on Brexit was intended to frighten Britain into voting to remain in the EU. Ángel Gurría, its secretary-general, has tried to translate his figures into a blood-curdling soundbite about losing a month's salary by 2030 (something that could easily be remedied by a tax cut). Its finding is that the trade we'd apparently forfeit would make the UK economy 5pc smaller that it would otherwise be 2030, not quite so bad as the 6pc estimated by the Treasury. And by the OECD's maths, the "cost" to households is closer to £700 a year than George Osborne's made-up figure of £4,300 a year.
But because the OECD report is not as deceitful as the shameful document produced by George Osborne last week, we can see more of its working (the Treasury tried to cover its tracks). And the OECD’s assumption is that net immigration would plunge by about 84,000 by 2030: a Brexit effect. And the fall might be higher: 116,000. Or as low as 56,000. The 84,000 fall is a midway point.
Currently, the UK figures envisage immigration falling to 185k a year by 2020 - and every year thereafter (see graph, below). So if you believe the OECD, this this would be about 100k if Britain regains control of its borders. That is, pretty much, David Cameron's target – and about a third of today's levels.
So should we believe the OECD figures? Of course not. The idea of trying to forecast anything by 2030 is laughable – especially when the pointy-heads can't forecast GDP or migration even three years into the future.
But unwittingly, the OECD has today ended up handing ammunition for one of Vote Leave camp's core arguments: that if you want to control immigration and hit David Cameron's target of immigration under 100,000 then you need to vote to leave the EU.