Experiments involving animals remain an important part of scientific research in the UK.
The practice is a source of controversy - proponents pointing to the medical advances testing brings, while opponents believe alternatives need to be found.
Number of animal tests
There were just under 2.9 million scientific procedures carried out on animals in 2005, according to the Home Office.
Since 1976, there has been an overall fall in the number of animal experiments, but recent years have seen the figures creep up.
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The increases are mainly due to the growing use of genetically modified mice, which scientists are using to model human diseases, such as cystic fibrosis.
The vast majority of experiments take place on rodents. They are relatively easy to breed and keep, and share basic biology and chemistry with humans.
Dogs and cats are used much less frequently - in 2005, there were about 300 experiments involving cats and 5,400 involving dogs. Beagles are the most common breed of dog used.
In 1997, the government ruled no licences would be issued for use of great apes (gorillas, orangutans and chimpanzees) in animal research.
But primates, such as marmosets and macaques, are still used - mainly for testing the safety of medicines or neurological research. The number of non-human primates used in lab experiments in 2005 was 3,120.
Purpose of tests
Currently, the majority of animal licences are given for breeding, fundamental biological research, and studies into human or animal medicine.
The majority of this research is non-toxicological, including work on immunology, drug research and development, cancer and genetics.
Some animals are used to test whether a product is safe for humans. These toxicological tests cover safety and efficacy of medicines, chemicals used in industry and agriculture, foodstuffs and the evaluation of environmental pollution.
Cosmetic testing has been banned in the UK since 1997, and since 1995 no animals have been used to test tobacco or tobacco products.
Who does the testing?
Most research involving animals takes place in universities and in commercial organisations.
Any laboratory wishing to use animals in research needs to apply to the Home Office for a project licence, and any scientists carrying out the research need to also hold a personal licence.
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To be granted a licence from the Home Office, scientists must demonstrate that there are no animal alternatives that could be used, any adverse affects can be weighed up against potential benefits, that pain and suffering will be minimised, and care and welfare are ensured.
In the UK, about 230 premises have a licence to carry out animal research, and some 14,000 scientists hold personal licences.