Using the patented technique, scientists can alter a gene in rodents and make them more likely to develop tumours, which means they can be used to test whether a material might contain carcinogens.

Spokesman Rainer Osterwalder said the EPO had decided that Harvard University's so-called Oncomouse patent would now only apply to mice rather than any kind of rodent.

The decision came after an appeal against the patent, the first ever granted for a transgenic animal, was launched by six organisations from Austria, Britain, Germany and Switzerland.

The ruling appeared to back their claim that the patent tried to protect animal varieties, which is illegal under the European Patent Convention.

The six had also maintained that it was "contrary to public order and morality" and did not meet other patent law requirements.

The ruling means that no new appeal can be launched except through the courts. The patent has been in force in the United States since 1988.

The environmental group Greenpeace, which was not involved in the appeal but had protested against the patent at EPO headquarters in Munich, southern Germany, said the decision did not go far enough.

The EPO is responsible for the practical functioning of Europe's patent system, which involves the 28 countries that have signed up to the European Patent Convention.

TERRA.WIRE