The number of people working excessive hours has risen by 15% since 2010, according to the TUC.
The TUC analysis reveals that the number of employees working more than 48 hours per week has now reached 3,417,000 - up by 453,000 since 2010, following more than a decade of decline in long hours working.
It warns that regularly working more than 48 hours per week is linked to a significantly increased risk of developing heart disease, stress, mental illness, strokes and diabetes.
TUC general secretary Frances O'Grady said: "Britain's long hours culture is hitting productivity and putting workers' health at risk."
According to the research, many people are working unpaid overtime and at least a million say that they want to cut their excessive hours.
Those working long hours are still disproportionately men (2,544,000 men compared to 873,000 women in 2015) but the number of women working 48 hour plus weeks has increased by 18% since 2010, compared to a 15% increase in the number of men.
The TUC is calling on the Government to reassess its negative view of the EU Working Time Directive, which has been brought into UK law and stipulates a 48-hour working week. Many long hours employees report that they feel pressured to "opt-out" from the 48-hour limit as a condition of employment (individual opt-outs are currently allowed by law).
All areas of the UK have seen an increase in the number of long-hours workers but Yorkshire and the Humber has seen by far the biggest increase with 30% more employees working over 48 hours a week in 2015 than in 2010. There have also been big increases in Wales (22%) and London (21%).
The growth in long hours has impacted differently on various industries. The biggest increases have been in mining and quarrying (64%), agriculture, fishing and forestry (43%), accommodation and food services (36%), health and social work (32%) and education (31%).