People who call for a better balance between work and home life are being accused - by one of the big employers' organisations - of creating myths in order to push through changes in working practices.
Men in the UK work an average 40 hour week
In a special report, the Institute of Directors (IoD) said that most UK workers who put in long hours did so voluntarily or to further their careers.
But union leaders dismissed the findings.
"If the IoD are right, millions of workers would be clamouring outside their work places today demanding
to be let in and furious at being forced to take a bank holiday off," said Brendan Barber, the TUC general secretary elect.
The report's author, Ruth Lea, said that despite claims that the UK had a "long hours culture" and was full of "overworked workaholics", official figures showed that the average full-time male employee worked fewer than 40 hours a week.
British employers... are some of the most flexible in the world
The average woman worked fewer than 35 hours a week.
Ms Lea said it was not true that people in the UK worked the longest hours in Europe because Greeks worked longer hours.
And she rejected claims that British working practices were inflexible, pointing out that 40% of women worked part-time, compared with an average of 28% across the EU.
"British employers... are some of the most flexible in the world.
"But the work-life balance protagonists ignore this and run an anti-business agenda that seems hell-bent on demonising the workplace with a collection of, for want of a better phrase, 'urban myths'."
She said the work-life balance agenda was behind many of the government's family friendly regulations which made it even harder to run a business in Britain.