Animals were used in a little more than 3.2 million medical experiments in 2007, a six percent rise from the previous year, the government said on Monday.
The increase was the sixth consecutive annual rise, according to figures released by the Home Office.
Most of the animals used in the experiments were mice, rats and other rodents. Less than one percent included dogs, cats, horses or non-human primates, the government said.
The rise was due mainly to breeding genetically modified animals - mostly mice and fish. By turning off or inserting genes in animals scientists hope to improve understanding of human diseases and to develop new treatments.
Drug companies say animals are a vital part of the research and development of new medicines and vaccines.
Animal rights groups who have fought a campaign against the experiments say the figures mark a 16-year high.
