The survey found that more than 50% of employees do not get paid for the additional hours spent at their desks and nearly 75% do not take their full lunch break entitlement.
Such high levels of over-service mean that some UK companies are getting an extra eight working days a year per employee.
"Putting these figures into perspective, for every working week, 13% of employees are giving an extra half a week for free," said Bob Stream, head of WRQ UK. "It is as if these British workers are giving their employers supermarket style offers - buy two weeks and get the third free.
"In monetary terms, this equates to more than £12,000 of 'free labour' per employee each year, based on the average gross hourly earnings of £11.73 per hour [Office For National Statistics, April 2002].
"Even for those employees working just one extra hour a day, this totals more than 30 working days a year - well in excess of most people's holiday entitlement."
According to WRQ, technology is a root cause of the high rates of overtime among UK employees. The survey found that inefficient technology has over-burdened the increasingly stressed office worker. Also, many companies rely on large numbers of disparate, older IT systems that can require time-consuming labour.
The overtime situation was found to be significantly worse for employees in the Midlands, Wales and the south of England, where almost one quarter (24% in the Midlands/Wales and 22% in the South) work on average at least 2.5 extra hours a day, compared to just 10% of office workers in the north of England and Scotland.
WRQ's research also found that older workers are worse off when it comes to overtime pay. Although 47% of the 16- to 24-year-olds questioned said they receive additional salary for any extra hours worked, only 13% of 55- to 64-year-olds do so, with 71% never receiving extra pay for overtime.