The controversy over unreliable climate change studies has intensified after the scientist at its centre faced fresh accusations that he tried to withhold data that could cast doubt on evidence for rising world temperatures.

The charges follow an analysis of the emails hacked from the University of East Anglia's Climatic Research Unit, of which Professor Phil Jones is the director.

The emails, published online on the eve of the Copenhagen climate summit, led to allegations that Professor Jones and other researchers had behaved inappropriately in withholding or deleting scientific information to prevent its disclosure under the Freedom of Information Act.

Last week the charge became more serious when the Information Commissioner's Office said that in withholding information, the university had broken the law. The university has set up an independent inquiry into the affair, headed by Sir Muir Russell, a former vice-chancellor of Glasgow University.

But the new allegations go beyond refusing requests under the act and concern data that Professor Jones and other scientists have used to support a record of recent world temperatures that shows an upward trend.

Climate sceptics have suggested some of the higher readings may be the result not of a warmer atmosphere, but of the so-called "urban heat island effect", where cities become reservoirs of heat and are warmer than the surrounding countryside, especially at night.

Professor Jones and a colleague, Professor Wei-Chyung Wang of the State University of New York at Albany, suggested in an influential 1990 paper in the journal Nature that the urban heat island effect was minimal - and cited as supporting evidence a long series of temperature measurements from Chinese weather stations, half in the countryside and half in cities, supplied by Professor Wei-Chyung.

The Nature paper was used as evidence in the most recent UN report on climate change.

But it has been reported that when climate sceptics asked for the precise locations of the 84 stations, Professor Jones at first declined to release the details. And when eventually he did release them, it was found that for the ones supposed to be in the countryside, no location was given.

Climate sceptics are demanding the two professors withdraw their heat island paper.