The Government will take the first step today towards passing controversial legislation that will lead to more than 150 NHS organisations being scrapped.
The Health and Social Care Bill has attracted widespread criticism from unions and policy experts worried that the reforms are "too much too soon".
Under the plans, GPs will be handed the bulk of the £100 billion health budget to buy-in services for patients and a new NHS commissioning board will oversee the process.
All of England's 152 primary care trusts (PCTs) will be scrapped alongside 10 strategic health authorities (SHAs).
PCTs are already being streamlined into "clusters" as part of the transition, with the aim of getting them to work with GP practices and emerging "GP consortia".
The NHS commissioning board will formally establish consortia from April 2012 but experts have warned that PCT staff are already leaving in droves, leading to concerns about patient services in the interim.
Leaders of major health unions have also queried how the NHS will implement the changes at the same time as finding £15 to £20 billion in "efficiency savings" - something no major health service has ever managed.
Doctors' and nurses' leaders have joined unions in warning that plans to create greater commercial competition between the NHS and private firms are "potentially disastrous".
RCN chief executive Dr Peter Carter said today: "This seminal bill has the potential to transform the NHS, however, at the same time as the service is being tasked with saving £20 billion, we are concerned that the proposed reforms are too much too soon.
"We will be studying each and every clause of the bill to make sure that the reforms deliver better care for patients.
"Nurses will have a pivotal role to play in the proposed new NHS structure, and we call on the Government to listen to their concerns.
"It is nursing staff who spend the majority of their time directly with patients."
On Monday, Prime Minister David Cameron strongly defended the Government's reform of public services.
In a keynote speech, he flatly dismissed the idea that the NHS could carry on as it was, supported by small amounts of additional public spending, as a "complete fiction".
He rejected suggestions that the Government was trying to do "too much at once" in pushing through reform.
"Pretending that there is some 'easy option' of sticking with the status quo and hoping that a little bit of extra money will smooth over the challenges is a complete fiction," he said.
"Put another way: it's not that we can't afford to modernise; it's that we can't afford not to modernise."
A strongly worded report from MPs yesterday said the Government's plans introduce "significant institutional upheaval" without really changing its aims.
Ministers have failed to show the plans represent the most "efficient" way of delivering good patient care, while some risks to the health service will increase, said the cross-party Commons Health Committee.
While supporting the overall direction, MPs said they were "surprised" by the "significant policy shift" between what the coalition promised to do in May and the plans set out in its health white paper in July.
The coalition outlined an "evolution" of existing bodies in the NHS but the white paper "proposes a disruptive reorganisation of the institutional structure of the NHS" subject to little prior discussion.
Peter Walsh, chief executive of Action against Medical Accidents (AvMA), said today: "We are not interested in the ideology behind these reforms, but are concerned about the potential impact on patient safety.
"The National Patient Safety Agency, once the envy of the international patient safety world, is already barely functional.
"There is no coherent plan for patient safety in the transition period and no clarity on how patient safety will be built into the new arrangements."