Quality of care for patients could suffer as the NHS struggles to make £20 billion in efficiency savings, health experts have warned.

Two-fifths of NHS finance directors expect patient care to worsen over the coming years, according to a survey.

Almost two-thirds think that the NHS as a whole will struggle to achieve the £20 billion "productivity challenge" by 2015, according to The King's Fund research.

Financial directors are confident they will end this year in surplus or break even, but monetary pressures will start to bite next year, the research suggests, as the two year public sector pay freeze comes to an end in April.

The report stated that an average staff pay increase of 1% would add around £400 to £500 million to NHS expenditure.

Professor John Appleby, chief economist at The King's Fund said: "The NHS continues to perform well in the second year of the productivity challenge. But there are signs that future years will be harder.

"The end of the public sector pay freeze next April may add to financial pressures and increase the strain on services.

"The difficulty for local providers will be finding ways to absorb these costs without compromising the quality of care for patients."

The survey of 45 NHS finance directors, who work across the sector, also indicated that there is growing pressure on emergency care.

The number of patients who are waiting for more than four hours in accident and emergency is at its highest level in the three month period from April to July since 2004/05, the researchers found.