More than five million British workers do unpaid overtime work beyond their contracted hours, according to new research from the TUC, meaning that they are giving employers the equivalent of £23bn of free work every year through unpaid overtime.
Top civil servants, corporate managers and CEOs do the most unpaid overtime, 12.5 hours a week. This means that they are effectively working for free until 27 March every year.
Teaching professionals are next with an average of 12 hours a week, followed by farm managers and health professionals, such as doctors.
Shelf fillers and telephonists are least likely to put in free overtime, although they still work up to an extra 2.2 hours a week.
Last year, a survey by recruitment consultancy Robert Walters found that a third of executives said that they are expected to work 10 or more hours a week without extra pay. A further half were expected to work between three and eight additional hours, while only one in five got away with putting in two hours or less non-paid overtime.
The TUC research, in the form of a new league table that allows workers to compare unpaid overtime, has been launched as part of a TUC campaign to highlight long hours,
The TUC has also designated 27 February as "Work Your Proper Hours Day" - the date when the average UK worker who does unpaid overtime finishes the 40 unpaid days they do every year and starts earning for themselves.
"We're not calling on Britain to turn into a nation of clock-watchers," said TUC general secretary Brendan Barber.
"But too many of Britain's bosses who depend on the unpaid overtime of their staff take it for granted and never show their appreciation."
The side-effects of long hours, such as stress and ill-health can be damaging for workers, he added, while long hours can also wreck relationships and make caring for children more difficult.