Employees did 23 billion of unpaid overtime; managers, professional staff and farm workers did some of the longest hours, the TUC said.
The union organisation urged people to work their proper hours and take regular breaks. It called on managers to treat their staff to drinks, or even a meal, as a thank you.
Teachers and lecturers were working 11 hours 36 minutes a week unpaid, two hours more than corporate and top managers.
Because of their higher rates of pay, senior managers’ overtime was worth an average of 19,000 a year, the TUC calculated.
In contrast, farm workers were toiling for almost nine extra hours a week without pay, worth just 2,500 a year.
The TUC has dubbed tomorrow Work Your Proper Hours Day as it would be the first day the average "long hours" employee would get paid if all their unpaid overtime was at the start of the year.