Ministers have been accused of "burying good news" about the NHS because it will undermine their case for sweeping reforms, after it emerged that they are withholding unpublished polling data that shows record levels of satisfaction with healthcare.

The Observer has learned that the polling organisation Ipsos MORI submitted the results last autumn to the Department of Health for inclusion in a government survey of public perceptions of the NHS. The data, commissioned by the department, shows that more members of the public than ever believe the NHS is doing a good job – a finding contrary to health secretary Andrew Lansley's insistence that it is falling short and needs urgent change.

The department has had the findings for six months, but has yet to make them public – the most recent information on its website relates to 2007. The decision to "sit on" the positive information has fuelled a row over the way in which the government is rooting out negative statistics about the NHS to justify reforms. Under the plans – rejected by the Liberal Democrats at their spring conference last weekend and opposed by a small band of Tory MPs, as well as by the Labour party – GPs will be handed control of £80bn of the NHS budget, tiers of management will be swept away and the private sector will play a greater role. The department was unable to say yesterday when it would publish the new data, but sources confirmed that the information shows public satisfaction at a record level.

In January, John Appleby, chief economist at the King's Fund thinktank, questioned the way in which ministers were unfavourably comparing the NHS with France. Appleby's article for the British Medical Journal attracted support from several academics and doctors. Professor Raj Bhopal, of the University of Edinburgh, said: "Justifying NHS reforms by picking a few statistics that cast doubts on the UK's renowned healthcare system is worrying, but choosing statistics that are widely questioned reminds me of previous government briefings that led to dodgy dossiers."

Labour's health spokesman, John Healey, said that it was clear the department did not want to put out good news because it would embarrass ministers trying to stem criticism of the Lansley plans.

Shirley Williams, the Lib Dem peer, said she was angry that the department had "cherry-picked" information – much of it from 2006 – before the extra billions poured into the health service by Labour had begun to take effect. In its 2007 public perception survey, also compiled from Ipsos MORI data, the department reported satisfaction levels at 63%. Then, last December, the British Social Attitudes survey found satisfaction at a record high of 64%.