Ed Miliband is launching a broadside at celebrities who make light of mental illness, as he unveils plans to tackle what he terms "the biggest unaddressed health challenge of our age".
The Labour leader will criticise writers and TV personalities Jeremy Clarkson and Janet Street-Porter for articles which he claims insulted and belittled people with mental illness and contributed to a national taboo on the issue.
Many people in Britain could get treatment for mental problems but are "intimidated" from seeking help by the fear of being mocked and subjected to "lazy caricatures", he will say.
Failure to tackle the taboos and address mental health issues is blighting the lives of millions of people, adding £10 billion to annual NHS spending and costing business £26 billion a year in reduced productivity, sickness absence and the cost of replacing staff who can no longer work, he will warn.
In a high-profile speech in London, Mr Miliband will say: "One in four of us will have a mental illness at some point in our lifetime. It is the biggest unaddressed health challenge of our age.
"There are so many people in Britain today who could be treated but who are intimidated from seeking help. And so many people who need support but who believe that no-one will care. It is a taboo which not only blights the lives of millions but also puts severe strain on the funding of our NHS and threatens Britain's ability to pay our way in the world. It is a taboo which must be broken if we are to rebuild Britain as one nation.
"There are still people who abuse the privilege of their celebrity to insult, demean and belittle others, such as when Janet Street-Porter says that depression is 'the latest must-have accessory' promoted by the 'misery movement'.
"Jeremy Clarkson at least acknowledges the tragedy of people who end their own life but then goes on to dismiss them as 'Johnny Suicides' whose bodies should be left on train tracks rather than delay journeys.
"Just as we joined the fight against racism, against sexism and against homophobia, so we should join the fight against this form of intolerance. It is not acceptable, it costs Britain dear and it has to change."
Mr Miliband will announce the creation of a taskforce headed by the chair of Barts NHS Trust, Stephen O'Brien, to draw up a strategic plan for mental health in society. He will promise to rewrite the NHS constitution to give patients the same legal right to therapies for treating mental illness as they already have to drugs and treatments for physical illness.