By Ian Dunt
Nick Clegg has promised "substantive" changes to the NHS reform bill, as he tried to steady his party over the issue.
The weekend saw one of his closest advisers, Norman Lamb, threaten to quit if NHS workers were not convinced by the government's plans.
The prospect of such a mass change of heart appeared bleak this morning, after the Royal College of Nursing (RCN) revealed that cuts to frontline clinical staff were likely to take place in the NHS, further increasing the temperature in an already heated debate.
Andrew Lansley will become the first health secretary for eight years not to speak at the RCN conference this week, as he seeks to avoid the fate that befell Patricia Hewitt several years ago, when she was booed and heckled by the audience.
"There's no point having a pause unless you're prepared to make substantive changes at the end of it," Mr Clegg told the Today programme.
But the deputy prime minister said there was a limit to how much of the bill the government was willing to change.
"We're not saying - Norman's not saying, the Liberal Democrats aren't saying - that we're going to reopen the Pandora's box of the basic design of the new system," he said.
"The basic building blocks are still in place. But the detail of exactly how that works in practise are the thing you want to get right."
Mr Lamb's warning presented Mr Clegg with his most alarming threat over the weekend, when he told the BBC's Politics Show that he was prepared to step down over the issue.
"I've said that if it's impossible for me to carry on in my position, I will step down," he said.
"And I think that it's in the government's interest to get it right in the way that I suggest."
Shadow chancellor Ed Balls said the remarks were "very significant".
He said: "Clearly Norman is very close to Nick Clegg, he's his closest political and parliamentary adviser. He made a very important point, which is that we shouldn't see reform as always good. These are bad reforms."
RCN research of 21 NHS Trusts published today shows that half of the posts threatened by spending cuts are in the frontline areas like nursing and midwifery.
The union estimated that 40,000 posts are under threat, although many of these are expected to be lost to natural wastage rather than redundancies.
"Even during the good times, when the sun was shining and the money was flowing, these reforms would have been huge. Now, that the clouds of economic gloom hang over us, and the cupboard is empty, reforming the NHS like this begins to look very difficult indeed," RCN general secretary Peter Carter told delegates.
"Let me be very honest with you Congress. Despite the honourable principles behind the bill, it could well turn out to be the biggest disaster in the history of our public services - if organisations like the RCN are not listened to, and listened to now."
While the Department of Health (DoH) has been spared many of the cuts being implemented in other government departments, the rising costs of the NHS mean that a cap on income amounts to a real-terms spending reduction.
The research does not directly address the issue of NHS reforms, but it will contribute to the animosity many nurses feel towards the government.
Mr Lansley was reported to be avoiding the RCN conference altogether, but he has decided to appear in a listening capacity only.