MPs are to hold an emergency debate on the coalition's NHS reforms tomorrow in a last-ditch Labour bid to keep them off the statute book.
Shadow health secretary Andy Burnham secured the debate in an attempt to delay the passage of the Health and Social Care Bill, which faces its final test in the House of Lords this evening.
Peers are due to give the legislation its third reading after which it will return to the Commons where the Conservative-Liberal Democrat coalition has a majority.
But tomorrow's Commons debate could allow MPs to delay the Bill's progress until the Government publishes an internal assessment of the risks posed by the reforms to the NHS in England.
Labour leader Ed Miliband said: "In the debate tomorrow, the Government must come clean about the damage this Bill will do to the NHS and publish the risk register.
"If they persist in piling secrecy on top of broken promises, the public will be in no doubt that they want to hide the truth."
The 90-minute debate tomorrow will allow MPs to decide whether the transition risk register document should be published before the Commons considers the amendments to the Health and Social Care Bill made in the Lords.
The Information Commissioner has ruled the document should be released and a tribunal upheld the decision after an appeal by the Government to block its publication.
The Commons is due to consider the Lords' amendments tomorrow, in what could be the Bill's final parliamentary stage before it becomes law.
Mr Burnham's application to Commons Speaker John Bercow for an emergency debate on the issue was granted after Labour MPs rallied to back his call.
Meanwhile in the Lords former SDP leader Lord Owen was today spearheading an attempt to defer the third reading until the risk register has been published.
"Risks go to the core of this legislation," he told peers.
"The issue before the House is whether the risks of continuing with the legislation, and nobody believes there are not risks, are greater than the risks of stopping the legislation."
He has tabled a motion that shadow leader of the Lords Baroness Royall told fellow peers they had a "duty" to support this evening.
She said that, given the coalition majority in the Commons where the Bill will return next, a third reading tonight would "pretty much" seal the fate of the NHS.
In a blogpost on LabourLords.org.uk, Baroness Royall said: "Today is a critical day for the NHS.
"It is a day on which the Lords will have up to two final opportunities to have an impact on the future of the Health and Social Care Bill, a day on which because of the coalition majority in the Commons, the fate of the NHS will pretty much be sealed."
The British Medical Association (BMA) also urged the House of Lords to block the Health and Social Care Bill.
Dr Hamish Meldrum, chairman of the BMA Council, said: "Even at this late stage a number of peers are raising very serious concerns about this Bill, which are shared by the BMA.
"Today is the last chance for peers to stop it and we would urge them to do the right thing - it is still not too late.
"The Health and Social Care Bill is not fit for purpose and it would be far better for the NHS if it were withdrawn.
"We want the Government to work with healthcare professionals so an alternative solution can be developed, one which has the support of NHS staff and the public."