Ed Miliband has written to the House of Lords urging them to "kill the Government's health bill" as pressure grows on the coalition to abandon the reforms.
The Labour leader's letter accuses Prime Minister David Cameron of being "increasingly out of touch" over the future of the health service.
Both Mr Cameron and Health Secretary Andrew Lansley have been facing growing calls to amend or scrap the plan altogether.
Mr Miliband claims the reforms to the NHS will "import the model of the privatised utilities into British healthcare".
"On behalf of my Party, I want to extend this offer to peers of all parties and of none: we will work with you to stop this Bill damaging the NHS," he wrote.
"Recent weeks and months have shown just how widely the concerns about this Bill are shared - not just among patients and the public, but also among doctors, nurses and other NHS staff.
"The Government would have us believe that those who oppose this Bill are 'vested interests'. I think that is deeply insulting to people who have devoted their lives to working in the NHS and care about its future.
"I want you to know that Labour has made an offer to put party differences aside and work with the Government on reform objectives we all share, such as greater clinical involvement in commissioning and the funding of social care.
"But ultimately, the NHS is too important to stand back and let this Bill damage it. I hope we can all work together to protect the future of our National Health Service."
The letter comes just a day after three Conservative Cabinet ministers reportedly "rang the alarm bell" over the plans - with one apparently comparing them to the poll tax.
The website ConservativeHome warned the controversial planned shake-up was "electorally fatal" and that most of the plans should be scrapped.
There have been calls for Mr Lansley to resign but the politician has continued to defend the reforms.
The Government has already "paused" the Health and Social Care Bill and accepted dozens of amendments since it was first introduced.
But the concessions have failed to quell protests from professional bodies such as the British Medical Association and the Royal College of Nursing.
The legislation has already suffered one defeat since reaching the Lords and there are fears that the process could drag on into next month.


257 comments