One in four employees now routinely works more than 48 hours a week.

The findings, which were released today, showed a massive increase in the number of people affected by the "long hours culture".

Researchers concluded that government efforts to change the work-life balance had made "little or no effect to date".

A survey by the Chartered Institute of Personnel and Development found the proportion of people regularly breaking the 48-hour barrier had risen from one in 10 five years ago to one in four.

The news comes on the day health minister John Hutton will open a European working time directive conference.

The average working week is now 39.6 hours - a slight rise since 1998.

Women have seen their working week rise by three and half hours to nearly 34 hours on average.

There was some consolation for ministers; one in four people have cut back their hours to meet childcare commitments.

The institute said legislation on working hours is useless because of the opt-out for people working more than 48 hours a week.

"Some employers are asking staff to sign an opt-out clause simply in order to take the issue of long hours off the table," said Mike Emmott of the CIPD.

"The negative effects of working long hours are increasingly recognised.

"Most long hours workers report some kind of negative effect on job performance, one in four report damaging effects on their mental health in terms of stress or depression and many claim that long hours have put their relationships and health under strain."