A four-day working week is more productive for most staff and companies than the traditional five days, one of the biggest trials of its kind conducted in the UK reported on Tuesday.

Over 60 firms in Britain took part in the six-month experiment allowing almost 3,000 employees to work one day less per week while retaining the same salary.

Conducted between last June and December, it was organised by non-profit group 4 Day Week Global alongside the think tank Autonomy, the University of Cambridge and Boston College in the United States. It has been described as the world's biggest trial of a four-day working week.

The study found more than nine out of ten firms will continue with the shortened working week or plan to do so, organisers said in a statement. Just four percent will not extend it.

Productivity did not suffer from the lighter working weeks, with company revenue rising 1.4 percent on average over the trial. Revenue jumped 35 percent on average, when compared with similar periods from previous years.

The study also found that hiring increased and absenteeism dropped -- while the number of staff leaving fell sharply during the trial. In addition, researchers concluded that the overall health and well-being of employees had improved.

Significant increases were observed in physical and mental health, time spent exercising, and overall life and job satisfaction. Rates of stress, burnout and fatigue all fell, while problems with sleep declined.