Not since the 1987 release of Wall Street has one small cinema on Manhattan’s Upper East Side seen so many investment bankers queueing to see a film. On Thursday night two film-makers presented a screening of their documentary I.O.U.S.A, born out of the genre that includes Morgan Spurlock’s Super Size Me and Michael Moore’s Sicko.

This time, the US audience is invited to berate itself not for how much it eats or for the failings of its healthcare system, but for the debt that the world’s biggest economy has run up. In New York, Chicago, Los Angeles and Florida, the showings were sold out.

The film’s opening credits are numbers, showing the terrifying magnitude of America’s national debt estimated at a record $9.5 trillion (£5.1 trillion), which means $149,000 for every US family, or $32,000 each “before any of you even spend a dime”.

The documentary comes at a sensitive time. About 450,000 Americans are losing their jobs each week. Banks have tightened lending and many Americans are finding it hard to borrow more.

The film follows two unlikely heroes: David Walker, the former Comptroller General, and his geeky side-kick, Robert Bixby, head of the Concord Coalition, a group that promotes financial and fiscal responsibility.

The two men have been crisscrossing America over the past year, giving speeches at schools and town halls, trying to press home the national debt problem. Together, in a people carrier topped with a 3ft graphic showing the size of the national debt, the two have embarked on their “Fiscal Wake-Up Tour” across 21 states. Their aim is to educate the American public and urge them to start a debate in Washington over reducing healthcare liabilities and raising taxes, to prevent the US being swamped by its overdraft.

Mr Walker tells the audience: “We suffer from a fiscal cancer. If we don’t treat it there will be catastrophic consequences.” He argues that the greatest threat to America is not a terrorist squatting in a cave in Afghanistan, but the US debt mountain. He is nervous about the increasing dependence on countries such as China, which are the biggest holders of US Treasury bonds.

Mr Bixby explains: “If you knew a levee was unsound and people were moving into that area, would you do nothing? Of course not.”

The two film-makers – married couple Patrick Creadon and Christine O’Malley - place the blame for America’s predicament at the door of President Bush, and Alan Greenspan, the former Chairman of the Federal Reserve. Speaking toThe Timesyesterday, Ms O’Malley, who co-wrote the film, said: “We don’t want to vilify. It isn’t just the problem of one Administration. But the record of the current Administration just speaks for itself - they have been horrible on this topic.”

Through interviews with former US Treasury secretaries Robert Rubin and Paul O’Neill and with Warren Buffett, the billionaire, the film argues that tax cuts introduced by Bush and the 12 interest rate cuts from the Fed since 2001 triggered a huge surge in borrowing that is now unmanageable.

“This is a toxic mix,” the film-makers claim. They argue that Medicare promises to Americans are unaffordable. “How much do we have to fund these liabilities? Zip,” says Mr Walker. “What good does it do to be the best-looking horse in the glue factory?”

The film makes a compelling case against Mr Bush: in an interview with Mr O’Neill, whom the President sacked, the former US Treasury Secretary claims that he was told “not to worry about deficits” and to support a programme of huge tax cuts. However, the film also points to a third culprit - the American people themselves, whom Mr Buffett urges to “live within your means”. During 2005 and 2006, Americans spent more money than they took home.

The film is to be screened at next week’s Democratic Convention, in the hope it will encourage voters to raise unpalatable issues such as tax rises and spending cuts. Ms O’Malley said: “No one gets elected on these issues. Politicians don’t want to talk about it.”

After Thursday night’s screening, beamed to cinemas across America, the documentary makers convened a debate attended by, among others, Mr Walker and Mr Buffett. The latter claimed to be optimistic about America’s outlook, saying: “I’m going to be the token Pollyanna here. There is no question that our children will live better than we did. But it’s just like my investments. I try to buy shares in companies that are so wonderful, an idiot could run them, and sooner or later one will. Our country is a bit like that.”

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