The NHS is expected to deliver 65% of its planned efficiency savings by year end, officials have told MPs.
The health service is expected to make £12.4bn in savings by April - which marks the halfway point of the four-year “Nicholson challenge” to make productivity savings by 2015.
During the first year, £5.8bn was generated but health analysts raised concerns that the first year of the challenge would be the easiest, with NHS managers “picking off the low hanging fruit”.
But by the end of the second year, the health service is ahead of schedule, David Flory, the deputy chief executive of the NHS, told the Public Accounts Committee.
“We are ahead of where we planned to be and certainly ahead of where the original plans were,” he said.
“If you think of the overall number of £18.9bn - by the end of year end I expect that the savings that will have been made will be £12.4bn which will be 65% of the total number.”
But MPs suggested that the figure was not a true representation of the productivity costs.
Conservative Stephen Barclay questioned: “How accurate is that figure if the trusts are reporting those savings in different ways? Some are not including one-off costs.”
Mr Flory replied: “It is gross of one-off costs.”
Sir David Nicholson, chief executive of the NHS in England, said there would be a number of “contentious” service changes emerging in the coming months.
Highlighting some service changes which have already caused public outcry, including the streamlining of children’s paediatric heart services and proposed changes to services in south London, Sir David said: “You will see no shortage of people wanting transformational change over the next few months.
“We are just coming into a phase now where there are quite a lot of fairly contentious service change issues emerging.”
He added that the productivity challenge is “necessary to do” to carry on providing free universal healthcare.
MPs also asked about reports that 17 NHS hospitals had unsafe staffing levels.
The Care Quality Commission issued the hospitals with warnings in November after carrying out inspections.
Sir David said the overall number of clinical staff had gone up across the NHS, adding: “There are hundreds of hospitals who manage to provide safe and secure staffing levels for their patients.
“All of those 17 have been asked to set out their plans for putting themselves back into a place where they have the staffing levels required by CQC.”