The number of people in the UK who work unpaid overtime has fallen for the fourth year in a row.
Top executives and officials work most unpaid overtime
According to the TUC, 4.76 million workers did unpaid overtime last year - a 6% fall since 2001.
The trade union organisation says teachers have been replaced at the top of the unpaid work league table by senior managers and officials.
45% of that group worked an average 12 hours each week unpaid, with their time valued at £24,000 a year per person.
The average amount of unpaid overtime among UK workers was 7.4 hours each week, for those employees who did them.
But such unpaid work is a feature of life for only a minority of UK staff.
In 2005 19.4% of the workforce worked overtime unpaid, down from 21% in 2001.
Those least likely to do any unpaid overtime were transport drivers, factory workers, road sweepers and refuse collectors, dockers, warehouse workers and construction workers.
As part of its continuing campaign against unpaid work, the TUC has designated Friday 24 February as "Work Your Proper Hours Day".
The organisation's general secretary, Brendan Barber, said the UK was beginning to cut its working hours.
"But there is still a long way to go before the UK gets anywhere near the European average," he said.
For workers in 15 EU countries, the average proportion of the workforce doing unpaid overtime was just 6.3%.
Only Austria (15.3% of workers) and Holland (17.8%) came anywhere near the UK experience.
Meanwhile in Ireland, Spain and Italy, employees who work unpaid appear to be virtually unknown - or at least uncounted.
In those three countries, fewer than 1% of their workers admitted to doing any overtime without pay.
Small business representatives, however, said the TUC was misguided in its campaign against unpaid overtime.
"The TUC, with this idea, is hurling a crowbar into the works of small businesses," said Nick Goulding, chief executive of the Forum of Private Business.
Small businesses provided jobs for a third of the UK workforce, and needed their staff not to be rigid about working hours, he said.
"The bottom line is small firms want a happy, productive and flexible workforce which understands the give-and-take nature of business," he said.