Rodents are the primary lab animal

Mice, rats and other rodents accounted for 84% of this total; fish and birds for much of the remainder. Dogs, cats, horses and primates combined accounted for less than 1%.

About 80% of all the experiments are for research and drug development; safety testing accounts for most of rest.

These figures have been broadly static for a number of years now and they are about half what they were in the 1970s.

They do not tell the whole story, of course. Many genetically modified animals, for example, whose DNA alterations fail are simply put down and their deaths not recorded in the official statistics.

Monkey brains

Neither are figures kept on experiments done on very lowly creatures like flies and worms.

Nonetheless, many important scientific advances have come from studies on animals such as the nematode worm because its simple genetic structure is relatively easy to probe.

ANIMAL-AIDED ADVANCES Antibiotics and vaccines Insulin for diabetes Treatments for leukaemia Local and general anaesthetics Anticoagulants Heart valve replacements Blood transfusion Kidney dialysis

Although mice and rats are the predominant animal choice in labs, they are not deemed suitable for all studies. Sometimes the way drugs work on their bodies is different from the effect they have on humans.

For this reason, some primates - almost exclusively marmosets and macaques - are employed in experiments; they are close living relatives and share much of our physiological fabric.

If a drug produces a particular effect on a macaque, so the argument goes, the chances are it will have a similar impact on a human.

In particular, scientists say monkey brains contain regions of higher cognitive function that are very similar to humans but are only poorly developed in other animals.

'Fundamental differences'

Professor Colin Blakemore, chief executive of the Medical Research Council, said: "Primates are, of course, special, and we strive to minimise their use.

"But studies involving primates have been crucial for our understanding of brain function, and have underpinned the development of brain scanning methods in people.

"Medical research with primates, including work at Cambridge, has led to important advances in understanding the brain and brain disorders.

UK ANIMAL EXPERIMENTS 2.73 million experiments in the 12 months of 2002 Total number of procedures rose by 4.2% on 2001 About 80% are for research and drug development Safety testing accounts for most of the rest Great apes such as chimpanzees cannot be used in experiments

"Current research in primates is offering hope of treatments for Alzheimer's, Parkinson's, Huntington's disease and strokes."

Opponents of animal research hotly dispute these claims, and say that similar advances would have been perfectly possible without having to inflict suffering on animals.

Andrew Tyler, of the animal rights group Animal Aid, said: "The fact that drugs are tested on animals does not mean that the tests are valuable, it just means that the tests have become a habit."

Animal welfare groups challenge many of the assumptions on which the science is done.

"There are fundamental differences in the structure of human and non-human primate brains," said Wendy Higgins from the British Union for the Abolition of Vivisection.

"There isn't similarity in all cases in different sub-species. In one Parkinson's disease model we reported on, the animal was continually circling - going around and around.

"Human Parkinson's sufferers don't do that but things like this are simply overlooked or it is hoped they can be factored out of the results."

Strict rules

Research on animals carried out in the UK is subject to strict rules designed to avoid unnecessary suffering.

To do experiments, scientists must get special licences issued under the Animals (Scientific Procedures) Act 1986.

And funding agencies may also have their own regulations. Before paying for research involving any animal, the MRC, for example, insists that the following conditions are met: