Scientific testing on live animals has fallen to its lowest level since 2007, official figures show.
Researchers carried out 3.52 million procedures on living animals in England, Scotland and Wales last year, a decrease of 7% from 2017.
Around half (1.8 million) of procedures were experimental, while the other 1.72 million were for the creation and breeding of genetically altered animals, data from the Home Office revealed.
The majority of procedures (93%) used mice, fish and rats, which have been the most used for the past decade.
However, the use of rats in experimental procedures fell by 27%.
The number of experimental procedures on birds increased from 130,000 to 147,000.
Specially protected species – cats, dogs, horses and primates – accounted for 1% (18,000) of experimental procedures.
The number of experiments with cats decreased by 20%, but the number using dogs rose 16%, and the number on primates increased by 8%.
More than half (56%) of experimental procedures were carried out for basic research – most commonly focusing on the immune system, the nervous system and cancer.
Procedures for creating and breeding decreased by 10%, while experimental procedures fell by 4%.
The data represents the number of procedures conducted on animals, not the number of animals that were involved.
Since 2014, the Home Office, which is responsible for regulating animal experiments, has classified testing according to the amount of suffering it causes.
Of the 3.52 million procedures performed last year, 38.9% were assessed as mild, 14.7% moderate and 3.6% severe.
More than two-fifths (40.2%) were considered sub-threshold – discomfort measured as less than a needle prick.
Understanding Animal Research, which promotes openness about animal research, released data showing 10 organisations account for nearly half of animal research in Britain.
They carried out 1.69 million procedures, 48% of the 3.52 million procedures in Britain in 2018.
More than 99% of these were carried out on rodents or fish.
The 10 organisations are the Medical Research Council, the Francis Crick Institute, the University of Oxford, the University of Edinburgh, University College London, the University of Cambridge, the University of Glasgow, King’s College London, the University of Manchester and Imperial College London.
All of the institutes have signed up to Concordat on Openness on Animal Research in the UK. They are also committed to the “3Rs” of replacement, reduction and refinement.
This means avoiding or replacing the use of animals where possible, minimising the number of animals used per experiment, and optimising the experience of the animals to improve welfare.
Frances Rawle, director of policy, ethics and governance at the Medical Research Council, said: “The use of animals in medical research remains essential for us to develop new and better treatments and to understand the biology of disease.
“If researchers are applying for funding for studies involving animals, they must give clear scientific reasons for using them and explain why there are no realistic alternatives.
“The MRC is committed to ensuring that these programmes are carried out to the highest possible levels of animal welfare and to replacing, refining and reducing the use of animals in research.”
Professor Julian Downward, associate research director at the Francis Crick Institute, said: “As the country’s largest biomedical research institute, we have a particular responsibility to be open about our use of animals in research.
“While we use alternatives wherever possible, living animals are incredibly complex and there are many processes we simply can’t simulate.”
In 2014 the way the animal procedures are measured changed to look at procedures that had concluded, and not those that had been started.
Dr Penny Hawkins, head of the research animals team at the RSPCA, said: “We sincerely hope that this fall in numbers reflects an ongoing trend.
“If it is due to increasing uptake of humane alternatives, and fewer animal lives being wasted when creating genetically altered animals, then this would be an essential step towards more humane science.
“But it is important not to become complacent.
“Behind these numbers are the lives of millions of individual animals. Each is sentient, and each is capable of experiencing pain, suffering and distress.
“The RSPCA strongly believes that these animals deserve much better, and that a lot more could still be done in practice to challenge animal use, reduce suffering and improve welfare.”