Prince Harry asks: What's the impact of mental health?
Is there a link between mental health and the nation's productivity? When Prince Harry was editing BBC Radio 4's Today programme, he asked us to look into this question.
On a building site in east London, men in hard hats and hi-vis jackets are putting the finishing touches to a block of flats.
The company doing the electrical work, RSE Building Services, was set up 14 years ago by Russell Stilwell.
As we chat in one of the almost-complete apartments, he tells me about a series of stressful and upsetting events that left him depressed.
Russell's best friend died. Then the company's biggest client went bust, owing more than £150,000. Shortly afterwards, Russell's father passed away.
"Getting up in the morning was becoming hard, being reasonable was becoming hard," he says.
Russell hit rock bottom; the emotional and financial stress was too much for him.
"I was carrying the people in my business, carrying my family and I couldn't cope. I was drinking, I snapped at my family, I became a monster... I was ill."
Russell's family told him to seek help, so he went to see his doctor and underwent months of counselling.
He's now happy, and his business is thriving again.
Russell's experience has led him to invest in new tools to make his workers' lives as stress-free as possible, by providing them with more accurate information than even on drawn building plans.
"We've brought in and invested in a lot of technology. It is removing the need for guys to be up on stepladders with tape measures. We use laser machines, which create clarity through their accuracy."
As well as that, Russell is involved in the Mates In Mind charity for construction workers. He tries to get his workers to open up and talk about their feelings - no easy thing in the blokey world of construction.
"We can reduce the macho culture that exists and mitigate the amount of mental health and wellbeing issues that exist in our industry."
"There's a business case as well. Productivity will improve by focusing on the wellbeing of our people and our people knowing their wellbeing is at the forefront of our culture."
Productivity is the biggest challenge our economy faces - tougher even than Brexit, say economists.
We need stronger productivity growth to get pay rises and for the nation to get wealthier.
We regularly talk about how wider roads, better broadband and new machines could make us more productive.
Is better mental health part of the answer to the productivity puzzle too?
Earlier this year, a government-commissioned review found that about 15% of people at work have symptoms of a mental health condition.
The Stevenson-Farmer Review put the cost of poor mental health to the economy as a whole at between £74 and £99bn a year.
The review also found 300,000 people with mental health problems lose their jobs each year.
"By looking after employee's mental wellbeing, staff morale and loyalty, innovation, productivity and profits will rise," says Emma Mamo, the Head of Workplace Wellbeing at the charity Mind.
It isn't just a case of caring for staff. In September, the Health and Safety Executive launched a campaign to remind employers they have a legal duty to protect workers from stress at work by doing a risk assessment and acting on it.
A psychological tech company, PSYT, has created an app to monitor and improve wellbeing in the workplace.
The company's Dr George MacKerron told me what they measure.
"We can figure out at different times of days, when you're with different colleagues, or you're doing different types of activity or there's been some kind of announcement or news within the organisation," he says.
"We can put that all in to our model and find out which of those things systematically affect everybody's happiness. We can say, 'If you were to invest a small amount of money in making people feel better in this way, you can expect a return on that investment of several times'."
A study by Deloitte has also concluded that companies which spend money on improving mental health benefit from that investment.
Research published in October 2017 found "The return on investment of workplace mental health interventions is overwhelmingly positive."
"We found that a 1% increase in happiness gives us a 0.5% increase in productivity," says Dr MacKerron.
"If you multiply that productivity gain by the revenue of the companies, the larger the organisation the bigger the savings that you make," he says. "Across the UK as a whole, we're talking tens of billions."
Sir Simon Wessely, Regius Professor of Psychiatry at King's College London, says the evidence is incontrovertible.
"Rather than quote all the studies that show that, it's easier to say I don't know a study that doesn't," he says.
"As the military says, you have to own the problem. If you are doing it in your own company, that does have a measurable impact of mental health...and productivity."
Mind's Emma Mamo agrees, "Many of the measures we recommend are small and inexpensive. Regular catch-ups with managers, flexible working hours, promoting work/life balance and encouraging peer support; can make a huge difference to all employees, whether or not they have a mental health problem."
The Stevenson-Farmer Review found that only four in 10 employers have policies or systems in place to support workers with common mental health problems.
I asked Russ Mould, investment director at brokerage AJ Bell, how seriously company chief executives take the issue of workers' mental health. He replied, "Physical health, very much so. Mental health, less so."
A firm which analysed all FTSE 100 annual reports found that "two out of three of Britain's biggest companies made no mention of mental health in their annual reports at all".
"On the upside we found that those that did, generated up to three times more profit than those that didn't," Soma Analytics said in a report in October 2017.
Russ Mould agrees. "It just makes perfect sense that if staff are engaged, if staff are happy, they're more productive and the firm does well."
Listen to a radio report on this story, edited by HRH Prince Harry, here.
Follow Rob Young on Twitter @robyounguk