An increase in the number of workers doing unpaid overtime in the public sector has almost entirely been driven by 250,000 more women working extra hours for free, according to a study by the TUC.
In 2003, more men than women did unpaid overtime in the public sector, but the position has been reversed, the research found.
One in four public sector workers puts in at least an extra hour a week, the TUC said.
Around one in six staff in private firms worked extra hours for no pay, a figure which has largely remained unchanged over the past decade, although the amount of unpaid overtime has increased.
More top news
A minute's silence will be observed at 11am on Thursday in remembrance of those who lost their lives in the Manchester Arena attack.
New research has found those who consumed two cups had a 35% reduced risk, and for those who drank five cups, the risk halved.
New research has found #Brexit was the most commonly occurring hashtag for abusive tweets.