The decline in NHS productivity, one of the reasons cited to justify the Government's controversial health reforms, is "a myth", it has been claimed.

The suggestion that productivity has declined over the past 10 years is inaccurate, according to Professor Nick Black, from the Department from Public Health and Policy at the London School of Hygiene and Tropical Medicine.

In an essay published by The Lancet, Professor Black said data showed productivity had risen, contradicting government claims.

The editor of the Lancet, Dr Richard Horton, said if the figures undermined the reasons for the controversial Health and Social Care Bill, the changes it would lead to were "entirely unnecessary."

He added: "This is further evidence to kill this damaging and dangerous Bill."

Prof Black said conclusions that hospital productivity has declined by 1.4% a year, and overall NHS productivity by 0.4% a year, were based on analyses by the Office for National Statistics based on estimates of changes in the quantity and quality of NHS care.

But these may have been underestimated because they were restricted to three aspects of health care. He said the major cause of concern was the estimate of quality improvement, which was judged to have risen by 0.8% a year. Professor Black said the improvement was actually considerably greater.

Health Minister Simon Burns said: "We have always been clear that productivity in the NHS needs to improve and are committed to better outcomes for patients across the country. We are investing an extra £12.5 billion in the NHS, but we want to make every penny count.

"We know the NHS can meet this challenge - we have already made £7 billion in efficiency savings over the last 18 months as performance has improved: record low infection rates, mixed sex wards down by over 90% and people waiting over a year reduced by half.

"We are modernising the NHS to put patients first, hand power to doctors and nurses, and reduce bureaucracy by £4.5 billion."