61 businesses across Britain took part in the study, Emma Simpson reports.

This is what a Friday looks like at environmental consultancy firm, Tyler Grange.

All the staff are off, they get 100% of their pay but do 80% of the hours.

What started as a trial is now a permanent switch.

We've seen our happiness go up significantly and we've seen our fatigue come down through the trial so we can prove that our team are happier, less tired and are making more money.

It's pretty cool.

So how did you do it?

Zero admin, I like to call it.

We're trying to get rid of as much of the admin as possible that you didn't need to do.

Our board meetings where it used to be two hours long, they're now half an hour.

If you give people this incredible incentive of a whole day of your time a week, they're going to work really hard to become more productive.

Just ask Linda, the office manager.

A day off for me is to get to do the things that I want to do, like this, the litter picking, doing something back for my community near where I live.

It gives me more time to reflect and be with nature.

Are you happier?

I am much happier.

Healthier?

Healthier. Definitely much healthier, as you can see, it gives us a little bit of exercise as well.

Could you ever go back to a five-day week now?

I wouldn't want to, no. I wouldn't want to, no.

It's something that I think more companies should take on.

The results are in for the 61 firms who took part in this six month trial.

39% of employees surveyed said they were less stressed.

There was a 65% reduction in sick days and companies who provided data said revenues stayed broadly the same.

Fewer hours on full pay may not be possible for every employer.

But with many companies finding it hard to attract staff and pay higher wages,

could this four-day week be a solution and help with the UK's long-running problem of low productivity?

I think this trial will be a game changer in terms of momentum in the UK toward a four-day week.

And I'm hopeful that it is going to spur more government interest in this, at all levels of government, and more experimentation and some support for companies who want to go forward

How to get the right work-life balance?

Fewer hours on full pay won't become mainstream any time soon, but this trial suggests there are alternatives to the traditional five-day week.

Emma Simpson, BBC News, Birmingham.