Labour leader Ed Milband has vowed to scrap the most controversial aspects of the Government's NHS plans if he won the next election.
Speaking to Sky News at the Royal College of Nursing Congress in Harrogate, he said: "There are many aspects of this Bill - the free market free-for-all, the allowance of half an NHS hospital's income to come from the private sector, and the conflicts of interest that we think have been created - that we have to scrap.
"We are not going to have another top-down reorganisation (to the NHS), so we will have to see what we inherit.
"But those parts of the Bill that introduce the free market concept, we will scrap."
Earlier, in a speech to nurses, he said that by working together they could help protect the NHS against "the damage" caused by the Bill.
He appealed to Health and Wellbeing Boards at the heart of the NHS changes to "act as the last line of defence in our NHS".
He said they should resist "the creep" of NHS charges for treatment and "put patients before profits".
He also launched a new campaign, NHS Check, to encourage staff and patients to blow the whistle on problems caused by the health reforms.
Mr Miliband received a standing ovation following his speech, a sharp contrast to the jeers and laughter during the address to Congress by Health Secretary Andrew Lansley on Monday.
A Department of Health source denied that there was a free market free-for-all in the NHS.
NHS hospitals have always been able to generate income from private patients, the source said.
A spokesman for Mr Lansley said: "This is an easy speech to make three years away from a general election. It is complete posturing."