The 'spiralling' costs of the Health and Social Care Act, will undermine patient care while creating significant upheaval, the RCN has warned.
Ministers estimate implementing the Act will cost £1.6 billion - £300 million more than originally predicted - provoking anger among nurses' and doctors' leaders.
Dr Peter Carter, chief executive and general secretary of the RCN said: 'The RCN has frequently stated its concerns over the bill - not only is it creating major upheaval, which will prevent the NHS from delivering quality care, it has done so at a huge expense.
'We were concerned that there would be hidden costs involved in such a large reorganisation and it is becoming clear that the government has not properly estimated just how much money this would cost. At a time when patient services are being cut and nursing jobs are being axed, this is a huge waste of money. What is of even greater concern is whether this cost will spiral further.'
Chair of BMA Council Dr Mark Porter described 'the huge costs of this largely unnecessary reorganisation' as being 'particularly galling', given the rationing of patient services.
'The NHS has been tasked with saving £20 billion by 2015, and that could go up,' he said. 'Achieving savings on this scale was always going to be a steep challenge, but it is being made even harder by the fact that time, energy and resources have been taken up by massive structural change.
He added that the Act was likely to result in greater fragmentation, leading to competition rather than co-operation and making it harder to achieve efficiency savings.
'It is difficult to believe that the changes will generate cumulative savings of £5.5 billion. While some costs have been reduced through frontloaded reductions in administrative spending, these are unlikely to be sustainable on the same scale in the longer term.'