Health Secretary Andrew Lansley is to launch a fresh attempt to explain the government's NHS shake-up in England amid claims the policy is in "chaos".
Labour leader Ed Miliband says there is "utter confusion" about the plans, which give GPs commissioning powers.
He said the "reckless" reforms risked destroying the NHS.
Mr Lansley will later rule out a U-turn, in a statement to MPs, but he will seek to clarify what the plans mean to doctors and patients.
The prime minister's official spokesman said: "We have a clear objective of reform and modernisation of the Health Service, and we intend to push ahead with those.
But he added: "There is a job to be done in convincing people of these reforms."
The spokesman said Mr Lansley would also be "setting out the next steps" for the controversial Health and Social Care Bill.
Prime Minister David Cameron and his deputy Nick Clegg are planning to launch a "listening exercise" later this week to reassure the public about the planned changes.
But many of Mr Clegg's own Lib Dem backbenchers are angry about plans - and have demanded a series of changes to the bill.
And Labour has accused the government of creating a "crisis of confidence" in the NHS with a "wasteful" and unnecessary reorganisation.
In a speech in London on Monday, Mr Miliband criticised plans to scrap primary care trusts and give GP consortia the money to commission services at a local level.
He said GPs could "play more of a role in commissioning", but the idea that we transfer all commissioning "lock, stock and barrel" to GPs "without it being properly tested, without the evidence... doesn't make sense".
Mr Miliband said Labour did see a role for private companies within the NHS, but the government's proposals "take us into a whole different arena" and are "ideological and reckless".