Judges have ordered the publication of a secret study which has raised fears that eating GM food may harm human health, after it was revealed in The Independent on Sunday last month.

A court in Cologne last week granted Greenpeace access to the 1,139-page study - by the giant biotech firm Monsanto - which found that rats fed a modified corn had smaller kidneys and raised levels of white blood cells and lymphocytes compared with those fed a non-GM corn.

The maize - code-named MON 863 - is expected to be approved for human consumption in Europe later this year. Professor Gilles-Eric Seralini of the University of Caen, who scrutinises the safety of GM products for the European Commission and French government, describes the findings as "very worrying".

Environmental groups in several European countries have been pressing for the report's publication for months. They intensified their campaign after The Independent on Sunday's disclosures, and the EC also called for the secrecy to be lifted.

Monsanto - which dismisses the differences between the rats as pure chance - supplied the study to safety authorities on condition it was kept confidential. It has consistently refused to make the study public, saying it "contains confidential business information which could be of commercial use to our competitors". Last week the dispute ended in a German court, where Greenpeace argued the study should be published under a European Union law, namely the public should have access to documents assessing GM risks.

The court agreed. Greenpeace hailed the victory as "an important success". Monsanto appealed. Tony Combes, UK director of corporate affairs, said: "Everyone who needs to see [the study] has seen it."

The company denies environmentalists' accusations that it is appealing to try to keep the study secret while European ministers decide next month whether to allow the corn to be sold for human consumption. If ministers cannot agree, the EC has made clear it will wave it through anyway, using a loophole in European law.

Dr Brian John, of GM-free Cymru, welcomed the court's decision and said it would be "irresponsible and cynical in the extreme" to pass the corn for human consumption.