Use of agency nurses in the NHS has led to lower efficiency after changes to shift patterns.
The claims come from personnel directors and Unison as the Government announced pay rises to help recruitment and retention.
Trusts are now reverting to traditional shift patterns and more family-friendly policies.
John Adsett, head of personnel at Basildon and Thurrock General Hospitals Trust, said there had been too much emphasis on the use of nurses supplied by agencies.
He said, "At one time we were all being preached at that you have to have a core workforce and a peripheral workforce.
"It was a fashionable theory for a while. It was at a time when we were told that what was good for industry was good for the NHS."
He added, "Part of the problem was that you had staff to whom the organisation was not particularly loyal because we only asked them in when there was a crisis. Consequently you do not get the loyalty.
"There are a lot of trusts that have had a long, hard look at things like working patterns and are trying to be as flexible as possible now."
Unison's head of nursing Karen Jennings said many nurses left for agencies because they were forced to work a full range of shifts under the internal rotation system introduced in 1995-6. They found agencies offered them more flexibility.
"For example many had previously chosen to work night shifts only, because it suited them. But with internal rotation everybody had to work all types of shifts."
Last week's pay rises for nursing staff range from 3.4 per cent for a nursing assistant to 7.8 per cent for an experienced staff nurse.
In 1995-6, health regions in England spent £163m on agency staff. The figure rose to £191m in 1996-7 and £216m in 1997-8.
Jennings added, "Agencies are part of nursing now, so if hospitals want nurses back, it is all about offering good career development, understanding their domestic arrangements and not being dogmatic about internal rotation."
By Helen Rowe