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 today criticise writers and television personalities Jeremy Clarkson and Janet Street-Porter for articles which he claims insulted and belittled people with mental illness.

Many people in Britain could get treatment but are "intimidated" from seeking help by the fear of being mocked, he will say. Failure to address mental health issues is adding £10 billion to annual NHS spending, he will warn.

Mr Miliband will say: "There are still people who abuse the privilege of their celebrity to insult, demean and belittle others, such as when Janet Street-Porter says 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'."

In a high-profile speech in London, 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.