Ed Miliband has criticised celebrities who make light of mental illness, as he unveils plans to tackle "the biggest unaddressed health challenge of our age".
The Labour leader criticised Jeremy Clarkson and Janet Street-Porter for articles which he claimed belittled people with mental illness and added to a national taboo on the issue.
He said many people in Britain could get treatment but were "intimidated" from seeking help for fear of being mocked and subjected to "lazy caricatures".
Mr Miliband warned failure to tackle the taboos and address mental health issues was blighting the lives of millions of people, adding £10bn to annual NHS spending and costing business £26bn a year in reduced productivity and sickness absence.
In his first major speech since he claimed the One Nation mantle of Benjamin Disraeli for Labour, he also argued that Britain could not be one nation if it writes off people with mental illness.
In a high-profile speech to the Royal College of Psychiatrists in London, Mr Miliband said: "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.
"For far too long our leading politicians have been far too silent about mental health, part of a taboo running across our society which infects both our culture and our politics.
"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 announced 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 promised to rewrite the NHS constitution to give patients the same legal right to mental health therapies as they have for physical illness.
Labour would ensure training for all professional staff covers mental health and would integrate physical and mental healthcare more effectively, he said.
"We can't prevent all mental ill-health. There are not cures for all conditions. But we can help change the culture in our country. We can insist that everyone counts. That everyone matters," he added.