Millions of workers are doing unpaid overtime, giving employers billions of pounds of free labour, research suggests.
A study by the TUC found that teachers topped a list of those putting in the most unpaid overtime at more than four hours a week, costing them an estimated £15,000 in lost earnings.
Teaching unions called it “daylight robbery”.
Patrick Roach, general secretary of the NASUWT, said: “The fact that teachers are at the top of the list of professions working unpaid overtime is yet further shameful evidence of the Government’s failure to invest properly in our schools and colleges.
“Teachers are seeing their workloads piled higher and higher and, with cuts to support staff and cuts to other children’s services, teachers are now working around the clock.
“Our latest research found that more than half of teachers polled worked more than 50 hours a week, with some working more than 70 hours.
“This is unsustainable and unacceptable. World-class education cannot be built off the backs of over-worked and underpaid teachers and headteachers.”
Daniel Kebede, general secretary of the National Education Union, said: “The Government has shot itself in the foot by failing to tackle working hours for so long.
“Unmanageable workload is the main driver of teachers leaving, alongside excessive accountability.
“Graduates look to teaching and the current education climate and unsurprisingly opt for other professions rather than be underpaid for excessive hours spent in buildings that are falling apart thanks to a miserly Government.”
The TUC dubbed Friday “Work Your Proper Hours Day”, urging workers to take the breaks they are entitled to and finish their shifts on time.
Managers were encouraged to support staff by setting reasonable workloads and putting in place workplace policies to protect against burnout.
The TUC said 3.8 million people did unpaid overtime in 2023, worth thousands of pounds a year for every worker.
Two out of five teachers did unpaid overtime, according to the report.
Other professions with high rates of unpaid overtime included health and social services managers.
TUC general secretary Paul Nowak said: “We’re encouraging every worker to take their lunchbreak and finish on time today, and we know that the best employers will support them doing that.
“Most workers don’t mind putting in extra hours from time to time, but they should be paid for it.
“Part of the problem is that some employers fail to record the overtime staff do and when they don’t record it, they don’t pay it.
“Conservative ministers know about this problem, but they refuse to tighten the rules on employers’ records.
“We all depend on public services but they’ve been run down by Conservative cuts and mismanagement.
“That’s why public sector workers do so much unpaid overtime.
“They are going flat out to provide the services families rely on but burnout and staff retention are big problems.”
Ruth Wilkinson, head of policy and public affairs at the Institution of Occupational Safety and Health, said: “The outcome of this survey is alarming. Working long hours without adequate rest and recovery periods can impact workers’ health and their safety, as well as impacting their ability to take care of responsibilities outside of work.”