British workers do an average of seven hours and six minutes, in effect of a full working day, of unpaid overtime each week, work that were they to be paid for would see them taking home an extra £4,800 a year, unions have said.
The analysis by the TUC has concluded that if everyone in the UK who worked unpaid overtime did all their unpaid work at the start of the year, the first day they would get paid would be Friday 23 February.
The union body has therefore branded that date "Work Your Proper Hours Day" and is urging employees to use it to remind bosses of their extra unpaid work by taking a proper lunch break and going home on time for this one day a year.
Employers and managers, it suggested, should also use the day to say thank you to staff for their unpaid work, perhaps by buying them lunch or an after-work coffee or cocktail.
Nevertheless, the TUC survey did find a reduction in the amount of unpaid overtime being carried out, albeit a relatively small 18 minutes less than that reported in a similar survey last year.
TUC general secretary Brendan Barber said: "We work the longest hours in Europe, and too many workplaces are gripped by a long hours culture.
"There are some small signs that we are getting a bit better, but there is still a long way to go."
A balance had to be struck between workers becoming "clock watchers" and their goodwill and desire to do a professional job being taken advantage of, he suggested.
Unpaid overtime often increases only gradually, with employees, a psychologist has argued, failing to realise how much extra time they are working, and the negative effect this is having, until it is too late.
Psychologist Dr Roy Bailey has said, while increased tiredness and irritability are early signs of overwork, these can be followed by health problems and family breakdown.
Workers may often be torn between complaining about extra hours and not wanting to lose the personal benefits they bring, such as more money.