Businesses should be forced to reveal how they help employees with mental health issues if they fail to disclose the information voluntarily, Vince Cable has said.

The Lib Dem leader told HuffPost UK the law should be changed to impact firms with 500 or more staff.

“Businesses must become far more transparent about how they help staff deal with mental health issues, as well as better measure key mental health indicators such as absences,” he said.

Cable was speaking ahead of his appearance today at the MAD World Summit in London – which focuses on mental health in the workplace.

Wednesday is world mental health day, and Cable said the Companies Act should be amended so employers have to report on workplace mental health.

“Only one in nine of our biggest employers disclose any information on mental health in their annual reports, according to Business in the Community, but they must because this will mean best practice is shared across industry and will improve the workplace for all employees,” he said.

“This transparency would also drive standards through competition, with large employers forced to prove that they are leading on an issue that is finally being more openly discussed in society.”

The Lib Dem leader added: “If big companies won’t voluntarily disclose this information or produce a thorough, publicly published plan of action, then the government should take heed of the Stevenson/Farmer review and amend legislation to force employers to do so.”

The Stevenson/Farmer ‘Thriving at Work’ report, commissioned by Theresa May, found 300,000 people with a long-term mental health issue lose their jobs each year.

According to the study, published in October last year, the annual cost to employers is as much as £42bn, with the total cost to the UK economy estimated at £99bn.

Cable is also pushing for companies to measure key indicators of mental health, such as staff absences and the findings of staff surveys.