Gordon Brown should throw open the government's books so that they can be examined by an independent body, said the Lib Dems' Vincent Cable.
Mr Cable is the Lib Dem Treasury spokesman
He told the chancellor in many respects he had a good story to tell in his pre-Budget report.
But Mr Cable blamed the Iraq war for the fact the Treasury was struggling to match tax revenues to public spending.
He quoted a report that suggested there was 50:50 chance Mr Brown would have to break his own "golden rule" of only borrowing to invest.
Mr Cable - newly appointed as Liberal Democrat Treasury spokesman - was speaking just after the chancellor had delivered a bullish statement about the state of the nation's finances.
Mr Brown insisted that the government's borrowing meant the UK's debt burden was lower than the average for the world's major industrialised nations.
But Mr Cable said: "In some key respects, the chancellor has a very good story to tell.
"We do have low inflation and low unemployment, we have had steady growth and a respectable level of public debt.
"In other respects the statement shows the chancellor at his worst."
Mr Cable went on to criticised new "tax gimmicks" which he said would only add to an already "overcomplicated tax system".
He said that there were a lot of "red faces" in the Treasury because they had got there figures wrong over the level of nation's debt.
He said that the deficit was £10bn higher at £37bn than Mr Brown had expected just a year earlier.