David Cameron's former director of strategy has called for a vote to leave the EU, saying membership "makes Britain literally ungovernable".
Steve Hilton, who was one of the PM's closest aides, attacked Brussels' "statism, corporatism and bureaucracy".
In an article for the Daily Mail, he said the PM's "relatively modest" reform demands had received "arrogant and dismissive treatment".
Mr Cameron said evidence was more important than people's opinions.
The PM was asked about Mr Hilton's comments as he unveiled a new Treasury report warning a vote to leave the EU could trigger a recession.
He said "everyone is entitled to their opinion" but added that the "evidence" he was presenting was "far more important than the view of one person or another person".
The Treasury report marks the latest in a series of warnings about the economic consequences of leaving, including from the Bank of England and the IMF.
In his article, Mr Hilton said "establishment stooges" were being "wheeled out to attempt to persuade us to stay".
He said "no-one really knows" what the economic impact would be, adding: "It's clearly ridiculous to claim that it's settled in either direction; there are risks whatever we do."
Mr Hilton, who left Downing Street in 2012 for a post at Stanford University in the US, was one of the driving forces behind Mr Cameron's flagship "Big Society" project.
He said the EU had "become so complicated, so secretive, so impenetrable that it's way beyond the ability of any British government to make it work to our advantage".
After a "pragmatic, non-ideological assessment", he said he had decided: "Membership of the EU makes Britain literally ungovernable, in the sense that no administration elected by the people can govern the country."
Leaving the EU would allow the UK to "regain control over our country's destiny" he said, claiming the EU was not interested in anything other than "superficial change".
In other EU referendum news, a prominent Conservative MP and EU exit backer accused her fellow Leave campaigners of handing out "deliberately misleading leaflets about the NHS".
Sarah Wollaston, who chairs the Commons Health Select Committee, said the "current preoccupation with exploiting the NHS" was a "cynical distortion which undermines the credibility of their other arguments".
Vote Leave has said it is standing by its claim that leaving the European Union could save Britain £350m a week, money is says could instead be pumped into the NHS.
The UK Statistics Authority has called the £350m figure "potentially misleading".
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