The survey showed that 43% of respondents work between 40 and 50 hours a week; 21% between 50 and 60 hours; and 6% work a massive 60- to 75-hour week.
Under Working Time Regulations introduced in 1998, staff should not work more than 48 hours a week unless they choose to sign an opt-out clause.
Mike Emmott, adviser on employee relations at the Chartered Institute of Personnel and Development, said the directive has had a negligible impact as there is no real pressure on individuals to change.
"Fifty per cent of long-hour workers [people that work more than 48 hours a week] say it is their choice to work these hours," he said, "It is not because they love their jobs but simply because the work is there."
Of the respondents, 42% said they were under constant pressure to deliver results or solve problems but 76% said they enjoyed their jobs most of the time.
Separate research carried out by the institute shows that the average profile of a long-hour worker is a middle-aged, married or cohabiting male employee, working in middle management. They are also likely to be earning good money and be a professional. Nearly 30% of them will be self-employed.
Emmott said people who regularly work more than 50 hours a week are likely to suffer from headaches, depression and raised blood pressure. Personal relationships have also been shown to suffer.