Women under the age of 30 work the most extra hours.

This is according to a Trades Union Congress (TUC) study, which reveals that 39 per cent of the under-30s notch up hours over and above their contracted duty.

Comparatively, only a quarter of men of the same age work over their hours for no extra money.

Brendan Barber, the TUC general secretary, warned employers may grow to expect unpaid overtime and said the trend could lead to ill-health.

He also suggested that as women get older and have children, they are no longer able to work overtime: “It is hardly surprising therefore that the senior levels of most organisations are male and that the gender pay gap stubbornly persists.”

The TUC recently revealed that media professionals are most likely to put in overtime at work.

ClickAJob chief executive Yngve Traberg said bosses could do more to ease the burden: “Flexitime, job sharing, working from home, there are many ways an employer can show consideration and still be sure of getting the job done.”