Trade payment terms have reached an average of 55.8 days, the highest level since 2001, according to a Dun & Bradstreet report issued yesterday.Thirty-nine per cent of payments are made at 30 days or more past terms.Big businesses are the worst payers. Companies with 500 or more employees are taking an average of 62.7 days to make their business to business payments.Big business payment days have blown out by 5.6 days since the December quarter, D&B said.Small businesses, with up to 50 employees, are taking just under 55 days to settle accounts.D&B chief executive Christine Christian said businesses facing tighter credit conditions and weaker cash flow from loose collection practices were vulnerable to the impact of an economic downturn.Christian said: "Companies are being denied their cheapest source of funding - their own."