Nearly 650,000 working days were lost as a result of depression last year, costing the economy £54.6 million, Holyrood researchers have calculated.

The Liberal Democrats have pledged to support the recruitment of 960 additional mental health professionals - an average of one for every GP practice in Scotland - to address "the damage that mental illness does to individuals and the wider economy".

Around 337,000 people in Scotland have reported depression which has resulted in working days off and economic loss, according to figures obtained from the Scottish Parliament Information Centre by the Lib Dems.

Party leader Willie Rennie visited therapy animals from Canine Concern Scotland in Edinburgh to outline plans to deliver a million additional treatment sessions each year.

He said: "This analysis from the independent expert Scottish Parliament Information Centre shows the enormous scale of the damage that mental illness does to individuals and the wider economy. 643,000 working days will be lost this year as a result of depression, which is just one mental health condition.

"Doctors, nurses, therapists and others working in mental health in Scotland are doing fantastic work. But waiting time targets for treatment continue to be missed and the SNP have cut the share of spending on mental health.

"Under our plan, every GP practice will be able to have an additional qualified mental health professional to support and treat patients. They will be able to provide one million treatment sessions. This will help people get back to work and achieve their potential, as well as increasing productivity in the economy.

"We have already announced plans to double the funding going towards child and adolescent mental health services. This will end the scandal of year-long waits for treatment and the fact there are no beds for them north of Dundee.

"Our mental health plan will be an important part of our costed manifesto. It takes into account the areas north of the central belt that have been neglected for far too long, and will deliver for children and adults across the country who continue to suffer from debilitating mental health issues.

"We will make sure that treating mental health as the poor relation stops in 2016."

Health Secretary Shona Robison said: "We've invested substantially in mental health services, but we know that demand is increasing and so more needs to be done to ensure people can get timely access to the most appropriate support they require - both in and out of hours.

"As we recently announced, we'll be investing £3.5 million in local initiatives to support mental health in primary care this year.

"This is a small part of the £150 million we are investing in the next five years to support the transformation of mental health services for the benefit of patients of all ages in our communities."