They may not have to clock in, but they don't know how to clock off.

Two-thirds of self-employed people control "when and how" they work, according to new figures released by the Central Statistics Office (CSO).

But self-employed people who have autonomy over their work schedules are more likely to work longer hours than those whose working times are decided for them, the results of the CSO's Quarterly National Household Survey for the second quarter of 2004 suggest.

Some 38 per cent of self-employed people who controlled their working patterns said they worked 45 hours or more each week. Of those self-employed who couldn't control how they worked, only 27 per cent reported working 45 hours or more.

Self-employed people worked an average of 48.2 hours a week, compared to an average of 35.5 hours a week for employees.

Over 10 per cent of employees indicated that they worked overtime, compared to 8.3 per cent in a similar survey conducted in 2001. Four in every 10 people who work overtime received no additional pay for the extra hours.

Women who work overtime were less likely to be paid for the extra work than men. Over 52 per cent reported that they were paid nothing for the overtime they worked, compared to 39 per cent of men.

Four-fifths of employees who worked overtime in education, a sector where the workforce is predominantly female, reported that they did not receive payment for the overtime hours worked.

Employees who worked overtime clocked up an average of 40.6 hours a week, compared to 35 hours a week for those who did not work overtime.

Flexitime is still beyond the reach of most employees, with over two-thirds having a fixed start and finish time to their working day.

Less than one sixth - 16.5 per cent - said they had the ability to vary their start or finish times, with employees in the construction and education sectors the least likely to have flexible working times and employees in public administration and defence most likely to be able to adjust their start and finish times.

Around 8 per cent of employees said their hours varied within defined time bands, but were unable to build up hours that could later be claimed back as time off.

Only 2 per cent of employees said they could claim back hours they worked outside their normal start and finish times, with only 1.7 per cent able to claim days back.