We have the details tonight of a major piece of government work on the cost of leaving the EU.
Leave campaigners are sure to call it taxpayer funded propaganda but when the Treasury paper is released tomorrow morning, it will kick off a big week in the EU referendum campaign that will end with President Obama giving his backing to the Remain camp when he visits the UK on Friday.
George Osborne says tonight each household in the UK will suffer if Britain votes to quit the European Union on June 23rd.
In 15 years time, outside the EU, the size of the UK's economy will be hit to the extent that every household will be £4,300 poorer than if we vote to keep our membership.
The figure comes from a document which a senior Downing Street official told me earlier was a "thorough assessment" of the risks of leaving.
The Treasury has looked at three scenarios of the UK's future relationship outside the EU: the EEA option like Norway, the bilateral trade option like Canada or the World Trade Organisation rules like Russia and Brazil have with the EU.
The £4,300 figure is based on the middle scenario: the bilateral trade deal, similar to the one Canada has recently signed.
George Osborne will also try to demolish the claim by the Leave campaigners like Boris Johnson and Michael Gove that we'd have more money if we stopped paying into the European Union.
The Chancellor will say the analysis of civil servants is that there will be a hit on the UK's public finances if we left.
In other words, it will cost the UK more money to leave than it would to stay and keep paying the £250million per week.
On Friday, Vote Leave said the UK could spend £360 million extra each week on the NHS rather than pay that money to the EU.
But research for News At Ten last week showed that to be a false claim.
George Osborne will set out his case during a visit tomorrow with other members of the Cabinet.
Earlier I blogged on new thinking on the Tory backbenches about whether Mr Cameron could stay as Prime Minister if he were to lose the referendum - which is now less than ten weeks away.
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