Cases of staff working unpaid overtime are more common in the public sector than the private, research suggests.
Analysis by TUC suggests over a quarter of public sector staff worked unpaid overtime last year compared to only 18.5% of people employed in the private sector.
Trade union leaders today claimed the public sector was benefiting from £11.6bn worth of free hours every year.
Over a third of education staff and a fifth of health and social care staff worked unpaid overtime in 2014, the analysis suggests.
Staff in London and the East Midlands put in the longest amount of unpaid overtime per week, followed by employees in Wales and the North West.
TUC general secretary Frances O'Grady said: 'Staff across Britain are continuing to work among the longest hours in Europe and are not even paid for much of the extra time they put in.
'Millions of workers go the extra mile every week, boosting the profits of companies across the country while they lose out on thousands of pounds from their pay packets. And this is on top of the fact that one in five jobs already pays under the living wage.
'Bosses who encourage long hours in the office should re-think their approach as stressed, over-worked staff are often unhappy and less productive.'
