A group of MPs has claimed that NHS trusts are spending more than £1bn a year on agency nurses as a result of poor planning.
The bill has grown by 40% in the five years to 2005 - despite the number of permanent nurses in the health service rising by a fifth over the same period.
The use of agency staff may also be compromising safety because 39% have not received basic life support training, according to the Public Accounts Committee.
The Department of Health insisted in 2001 that growth in the NHS workforce would reduce the demand for agency staff.
But although 55,000 extra permanent nurses were recruited between 2000 and 2005, total expenditure on temporary nurses rose from £795m to £1.098bn, the MPs' report found.
Chairman Edward Leigh said temporary staff can be useful for dealing with short-term peaks in demand and holidays.
However, spending has been running at "worryingly" high levels despite the financial crisis in the NHS.
"Most trusts are failing to plan for and manage their demand for temporary nursing staff," he said.
"Too many do not have the management information they need to employ temporary staff cost-effectively. And too many are relying on temporary nurses to mask their inability to manage their permanent staff properly."
The Tory MP for Gainsborough insists the problem is not simply wasting taxpayers' money, but could be putting lives at risk.
He added it was "sobering" to learn that 30% of permanent nurses have also not received basic life support training - which is supposed to be mandatory.