George Osborne has angered those campaigning to leave the European Union after he enlisted the independent economic forecaster to the pro-EU cause.
Delivering his Budget in the Commons today, the chancellor told MPs the Office for Budget Responsibility (OBR) had warned Brexit would lead to an "extended period of uncertainty".
But senior Tory backbencher David Davis said the UK instead would be better off it it was free of the "failing, shrinking and unstable European economy".
And other eurosceptics were unhappy at the OBR being dragged into the debate.
Osborne told MPs the OBR "correctly" stays out of the political debate and did not assess "the long term costs and benefits of EU membership".
But the chancellor added: "They do say this, and I quote them directly:
'A vote to leave in the forthcoming referendum could usher in an extended period of uncertainty regarding the precise terms of the UK’s future relationship with the EU.
'This could have negative implications for activity via business and consumer confidence and might result in greater volatility in financial and other asset markets.'
Vote Leave Chief Executive Matthew Elliott accused the chancellor of trying to "politicise" the OBR.
"There is one budget the Chancellor didn’t touch today – the £350 million of taxpayers’ money he hands to Brussels every week. Nor could he cut taxes like VAT which we’ve given up control of to the EU Commission," he said.
"Disappointingly, the Chancellor sought to politicise the OBR and drag it into his campaign to keep us in the EU despite the OBR making clear that it was not making a judgment about the referendum."
Tory eurosceptic Stewart Jackson also appeared unimpressed with Osborne's claim that the UK would be better off within the EU.
However Jackson was more diplomatic following the Budget statement. He told The Huffington Post UK: "In fairness it would have seemed odd not to mention the Brexit issue so I believe the Chancellor said as much as he could and should have said in order to keep the focus on some big announcements like the Lifetime ISA and sugar levy."
Davis, who speaks on behalf of the Grassroots Out campaign, said: "Those who want to scare the British people about the supposed risks of reclaiming our independence will not be successful. The real risks for Britain lie in remaining within the EU.
"Many of the ‘cloudy skies’ and ‘cocktail of risks’ the Chancellor speaks of originate from a failing, shrinking and unstable European economy.
He added: "The safer choice for Britain is to leave the EU, take control of our own affairs and create a more competitive, globally trading British economy. We can only do this outside of the EU – free from burdensome Brussels red tape, costly EU bailouts and expensive contributions to the EU budget."
"Our economy will be best served and the British people best protected from a stuttering European economy by spending or saving the billions of pounds we send to Brussels on our own priorities in our own country."
Today the White House confirmed President Obama would visit the UK in April, when he is expected to make the case for the 'Remain' campaign at a press conference with David Cameron.