"Reductions in animal use are now being reversed by the increased use of transgenic mice," he told Reuters. "The explosion in animal use really ought to be controlled."

Balls retired last month after nine years as head of the European Centre for the Validation of Alternative Methods, which seeks alternatives to using live animals in experiments.

Genetic manipulation, in which scientists breed animals with one or more genes deliberately altered, added or removed, was popular because it was an exciting new technology, Balls said.

"Fashion is very important in science...but we shouldn't just throw money into technology because it's fashionable."

Many experiments could be carried out on human cells in a test tube rather than on live genetically modified mice, he added.

But Philip Botham, head of human safety at agrochemicals group Syngenta, said it would be decades before scientists could give up the use of animals in long-term tests, such as assessing whether a substance causes cancer or harms an unborn foetus.

"If we were able to replace animals tomorrow and still protect human health, we would do it," said Botham. "You don't imagine we would like to keep all those expensive animal rooms going for the next 30 years if we could avoid it."

SCIENCE "OUTSTRIPS" ETHICS

Jane Smith, a consultant working with Britain's Royal Society for the Prevention of Cruelty to Animals, said genetically modified animals accounted for more than 20 percent of all animals used in testing in Britain in 2000.

"At the moment scientific developments are tending to outstrip the ethical debate," she said.

Earlier, European Commissioner for Research Philippe Busquin told the Brussels conference that "the three Rs" - reduction, replacement and refinement - were the basis of the EU's approach to cutting animal testing.

Last month, the European Parliament voted to ban cosmetics tested on animals, which animal rights campaigners estimated involves 30,000 laboratory animals every year in the EU.