The number of men working more than 49 hours a week in the UK is now above three million, according to a new report from the GMB trade union.
The union says almost one in four men work longer than the 49 hours the European Union sets as a maximum.
“Burn-out Britain is becoming a reality for more and more people,” said GMB General Secretary Kevin Curran.
The worst effects of the long-hours culture are felt in Kensington and Chelsea and the City, the union said.
Mr Curran said the situation was still bad for many people over the festive period.
“You simply can’t be at your best if you are continually working more than 48 hours a week, even during holiday time,” he said.
The UK is the only country in the EU where workers can opt out of the Working Time Directive.
This is currently under review, although the government has argued that more than a million people will lose out on paid overtime if they had to stop working available extra hours.
The third longest hours are being worked by men in Westminster (the London borough, rather than just the Houses of Parliament), with the most affected UK regions being the South East and eastern England.
Mr Curran added: “This kind of workhouse ethic will not increase productivity; in fact, it will leave workforces resentful and burnt out.”
Making up the top five areas with the longest working hours for men are the Scottish and Welsh rural counties of Aberdeenshire and Powys.
Overall, 24.2% of men in employment in England work more than 49 hours a week, says the GMB.
The figure for Scotland is 22.4%, Wales also 22.4%, and Northern Ireland 19.8%.
Women’s average working hours of paid employment are far lower, with 5.8% in England, 5.4% in Wales, 4.9% in Scotland, and 4.4% in Northern Ireland.
The GMB says this is because many work part-time, and others do unrecorded work in childcare.