The government has sacked an independent national health adviser for questioning in the Guardian whether the money for its mental health strategy was new or came from the existing NHS budget.

When Nick Clegg announced £400m to improve access to modern psychological "talking therapies" last Wednesday, David Richards, professor of mental health services research at the University of Exeter, told the Guardian that the money was not additional. Instead of being spent on training therapists, it could end up used to plug other gaps in the NHS, he said.

The case has echoes of that of Professor David Nutt, who was sacked by the then Labour home secretary Alan Johnson for publicly questioning drug policy.

Richards has been involved since 2006 in efforts to increase the numbers of trained therapists who can help the substantial numbers of people with anxiety and depression. For the last two and a half years, he has been a national adviser to the Department of Health's improving access to psychological therapies (IAPT) programme.

He said it had been explained at a meeting of the IAPT group just over two weeks earlier that the money would have to come from the existing NHS budget. "We were very disturbed when we found this out," Richards told the Guardian. "I personally feel very aggrieved that mental health is being used by this government to shore up its very poor opinion poll ratings and I don't want to be part of it."

In a letter to the paper today, Richards says his removal is "extremely disappointing". His comments and sacking resulted from his frustrated efforts to get an answer to three important questions, he says. He wanted to know to what extent the money would come from cuts elsewhere in the budget; what mechanisms there were to ensure every penny was spent on training and therapy; and what systems had been put in place to ensure existing funds were not slashed as NHS cuts bit.

Richards writes in his letter: "The questions are not a matter of mere detail but of vital import for the many thousands of people trapped in a cycle of untreated misery and fear."

There are potential problems in the interaction between the government and independent advisers from academia, he says, adding: "Politicians assume that independent advisers are just going to do what they are employed to do . There is a general issue about the use of advisers who come from a highly independent academic environment."

However, unlike Nutt, who objected to government policy, Richards says he was simply asking for clarification.

Richards's main achievement in the last few years has been the establishment of a highly trained group of around 1,500 psychological wellbeing practitioners, who deliver cognitive behaviour therapy-based, low intensity help to people suffering from anxiety and depression.

Their interventions are brief, but effective, he says – as recommended by the National Institute for Health and Clinical Excellence. They make up 40% of the 3,600 therapists trained in the past three years. The programme aims to eventually train a total of 6,000.

The shadow health secretary, John Healey, said: "Evidence from a range of independent experts gives lies to ministers' claims that the NHS budget will be protected next year. And this 'new' funding for talking therapies again appears to show them misleading the public."

Meanwhile, a thinktank founded by Iain Duncan Smith is criticising the government for failing to take account of the impact of family breakdown on mental health. The Centre for Social Justice says ministers should have assessed the impact of dysfunctional families on the mental health of children and adults.

Its report, which defines family breakdown as "divorce or separation, dysfunction or dad-lessness", says: "Working with the whole family not only prevents many children from being labelled as mentally ill but can also tackle the causes of their problems – often rooted in or sustained by the dynamics of family relationships."

Additional reporting by Nicholas Watt