Men with children are the most likely group to put in unpaid overtime, according to research by the TUC.

The organisation found that men with children put in an average of 8.3 hours a week over time. Women without children were the next most likely, ahead of men without children and working mothers.

The trade union body claims five million workers in the UK regularly put in more than their allocated number of hours, which would have cost employers £25bn in 2007 had they been paid.

"On average, fathers who put in unpaid overtime are doing almost an extra day a week. This can't be good for them, their children or wider society," said Brendan Barber, general secretary of the TUC.

The TUC is urging employees to work their proper hours and employers to thank staff for their dedication by taking them out for lunch.