Ministers have pleaded with peers not to wreck controversial health reforms in a series of votes in the House of Lords today.
The Government betrayed signs of anxiety as a two-day debate began which will culminate in an attempt by opponents to block or delay plans for a sweeping overhaul of the structure of the NHS.
Lord Owen, the former leader of the SDP, and Lord Hennessy, the academic and constitutional expert, will today call for the proposals to be referred to a special parliamentary committee, which would report in December.
They argue that the NHS and Social Care Bill, which hands responsibility for the vast majority of health spending to GPs and clinicians, is so complex that it has to be considered in detail.
But Earl Howe, the Health minister, wrote to peers yesterday, warning that any delay could kill off the Government's chances of turning the plans into law.
He said: "The House must have proper time to examine the Bill but the proposal put forward by Lord Owen could result in delay, which could well prove fatal to it. This is not a risk that I believe this House should take."
Meanwhile, Andrew Lansley, the Health Secretary, rebutted accusations by peers that the Bill would undermine his constitutional responsibility for the NHS.
He wrote to Lord Hennessy: "The Bill will enable us and the NHS further to improve services. It will not in any sense dilute my responsibility and accountability for doing so."
More than 100 peers are due to speak in the debate, which started yesterday and will end with the votes this afternoon. The Bill's Second Reading began as more than 60 leading medical professionals called in a letter to The Independent for ministers to scrap or substantially rewrite the reforms.
Meanwhile a survey of 1,890 psychiatrists found that only one in 10 believes the plans will improve patient care. The Labour peer Lord Rea, a former GP, urged ministers to oppose the plans outright because they ran counter to ministers' promises to stop "top-down" reorganisations of the health service. "Instead of having a Bill that was in a manifesto, we have a Bill that was expressly ruled out by David Cameron and subsequently in the Coalition Agreement," he said.
Baroness Thornton, an opposition spokeswoman, claimed the Bill would "fundamentally change the nature of the NHS" and turn "patient choice into shopping".
NHS patients will be able to pick consultant
NHS patients needing specialist treatment will for the first time be able to choose the consultant to whom they are referred, Andrew Lansley announced yesterday.
In a significant extension of patient choice, hospitals will be required to accept all "clinically appropriate referrals to named hospital consultant-led teams".
Patients will be able to travel to any part of the country to see the consultant of their choice and hospitals would be required to publish individual "success rates" for their specialists to help patients choose, the Department of Health said.
The announcement, timed to bolster public support for the Health and Social Care Bill during its Second Reading in the Lords, brings NHS patients into line with private patients who already have the right to choose a named consultant.
But it marks a divergence from past policy which prohibited named consultant referrals to keep down waiting lists.
Rating individual doctors' performance has also been rejected in the past on the grounds that modern medicine is a team activity and individual performance measures would be misleading.
Sir David Nicholson, chief executive of the NHS, interviewed in 2008, said: "It's the team that makes the difference, not the individual. The days of the heroic surgeon, like Sir Lancelot Spratt, are long gone."