Newly appointed health secretary Jeremy Hunt is under fire for past comments that the NHS should be "denationalised".
The attack on Hunt comes as he has also been asked to explain his endorsement of homeopathy, support for restricting abortion and a reported attempt to cut the NHS segment from Danny Boyle's Olympic opening ceremony.
In a letter to Hunt sent on Wednesday, Labour's shadow health secretary Andy Burnham quotes a passage from the 2005 book 'Direct Democracy: An Agenda for a New Model Party', co-authored by Hunt.
“Our ambition should be to break down the barriers between private and public provision, in effect denationalising the provision of health care in Britain.”
The book, written by Tory backbencher Douglas Carswell, was co-signed by several other Conservatives including education secretary Michael Gove, Treasury minister Greg Clark as well as Hunt.
Labour also highlight passages in the book which say the NHS is "broken" and seems to invoke the US insurance model of healthcare.
“Instead of tinkering with a fundamentally broken machine, it (the Conservative Party) should offer to update the model.”
“We should fund patients, either through the tax system or by way of universal insurance, to purchase health care from the provider of their choice."
Burnham said the "N" in "NHS" was under "sustained attack" from the government and has called for Hunt to "urgently clarify" his position on the health system.
“Never has an incoming secretary of state made such overt statements about replacing the NHS with an insurance system," he said.
"His obvious lack of belief in what the NHS stands for will be a huge worry to patients and staff. They have a right to know whether he stands by his earlier remarks."
However Carswell accused Burnham of being "wilfully misleading" with his attack on the new health secretary, and pointed out the chapter was written by him - not by Hunt.
He told The Huffington Post UK that the book calls for the continuation of NHS reforms put in place by Labour under Tony Blair, adding "we need the NHS and we need it to be free at the point of use."
Carswell pointed to other quotes from the book that express support for free healthcare, including.
"The aim of government should be to guarantee access, irrespective of people’s ability to pay, to essential services."
In 2009 David Cameron slapped down another signatory to the book, Tory MEP Daniel Hannan, for having "eccentric views" on the NHS.
Concerns have also been raised about Hunt's apparent support for homeopathy. In 2007 the then shadow minister for disabled people signed a parliamentary Early Day Motion (EDM) welcoming "the positive contribution made to the health of the nation by the NHS homeopathic hospitals."
The EDM said complimentary medicine could help treat chronic conditions including chronic difficult to treat conditions such as musculoskeletal and other chronic pain, eczema, depression, anxiety and insomnia, allergy, chronic fatigue and irritable bowel syndrome.
In 2008 the-then MP for South West Surrey voted for the abortion time limit to be reduced to 12 weeks from 24 weeks.
Labour shadow health secretary Diane Abbott told HuffPost UK following his appointment on Tuesday that Hunt’s "record on women’s right to choose is really concerning".
Hunt, while culture secretary, was also reported to have questioned Danny Boyle's wish to include a section on the NHS in his Olympic Games opening ceremony.
The Times reported that Hunt asked whether it was "really necessary" to highlight the health service given the controversy over Andrew Lansley's health reforms, but David Cameron decided the section should stay in.
Hunt's promotion from DCMS to the Department of Health came as something of a surprise, given he was nearly forced out of government over his handling of Rupert Murdoch's attempt to take over BSkyB.
The Department of Health told HuffPost UK they had yet to see Burnham's letter.