The number of animals used in UK labs for scientific experiments is now more than three million - a level not seen since the beginning of the 1990s.
Home Office figures show that in 2007, all procedures in England, Wales and Scotland used 3.1 million animals.
The year-on-year increase of 6% continues the recent upward trend driven mainly by the use of rodents in genetics experiments.
Mice and rats constitute more than 80% of all animals used in laboratories.
The remainder involve primarily fish, birds, and reptiles/amphibians.
Dogs, cats, horses and non-human primates receive special protection under the Animals (Scientific Procedures) Act 1986. These were used in less than 1% of all procedures.
Most procedures are for research and drug development; safety testing accounts for much of the rest.
Animal welfare groups criticised what amounts to the sixth yearly rise in succession, but scientists said the work was necessary if society wanted to find ever more effective treatments for debilitating diseases.
The number of animals used in lab experiments peaked in the 1970s with more than five million procedures carried out annually.
The statistics then fell rapidly during the 90s and 80s before picking up again at the start of the century.
Just over 3.2 million scientific procedures were started in 2007, a rise of about 189,500 (6%) on 2006.
The use of genetically modified animals – mainly mice - has more than quadrupled since 1995.
By adding or knocking out genes in animals, scientists can gain insights into the molecular flaws in humans that lead to illness. Although fewer in number than mice, fish are becoming a popular tool in this regard. Zebrafish, in particular, breed fast and are translucent, making it easier to track changes.
In the oft-contentious area of non-human primate studies, the number of procedures started on animals such as marmosets and macaques decreased by 6% compared with 2006. A total of 3,125 of these animals were used in 2007; although scientists warned that the increasing sophistication of some new drugs could lead to the figures rising in future.
At issue are the highly engineered bio-molecules that work in very specific ways in the human body, switching on or off individual actions. To fully understand the likely effectiveness of such drugs, scientists may want to use more of the animals whose biology is closer to humans than rodents.
Paul Matthews, a professor of clinical neurosciences at Imperial College, told the BBC: "The growth in the [pharmaceutical] industry is going to create pressure that may drive those numbers up and I would anticipate that that is a probable consequence. At the same time I should emphasise that there is considerable work to try to minimise the implications in primates."
Animal welfare groups have long argued that the numbers of experiments – although smaller than they used to be – are still too high.
They say that many procedures often give misleading or wholly useless information; and that scientists ought to make better use of alternatives.
RSPCA senior scientist Barney Reed said his organisation was "extremely dismayed" to see yet another rise.
"Scientists and the government repeatedly state that animals are only used where absolutely necessary," he added. "Yet with the numbers going up yet again the public will quite rightly question this statement."
To coincide with the release of the official Home Office statistics, the Dr Hadwen Trust, a medical charity which funds non-animal medical research, issued its own report into the statistical trends under the Labour government.
The Trust said the 21% rise in animals used in labs since 1997 represented a severe disappointment given the party's manifesto promises.
The charity's Wendy Higgins added: "It has resulted in an 11-year record of failure that has now seen the number of animals dying in British laboratories reach three million for the first time in 16 years. If the government doesn't take urgent action to implement a clear strategy to replace animals with advanced techniques, Labour's legacy for lab animals will be an appalling failure."
Researchers counter that whilst great strides are being made in the use computer models, tissue cultures and other alternatives – some animal experimentation will always be necessary to help find cures for life-threatening diseases.
Professor Roger Morris, the head of the School of Biological Sciences at Kings College, London, said: "We do an enormous amount of work in tissue culture; we have any amount of work in purified molecules - but only in an animal can we understand how a manipulation is going to get a response from a whole animal; from the immune system, from the nervous system, from the various physiological mechanisms - the liver, the blood and everything else.
"If you think you can do all that in tissue culture, you have no idea about the complexity of animals."
And Home Office Minister Meg Hillier said: "Advances with non-animal test methods continue to be made, but at present licensed animal use remains essential to develop improved health-care technologies. The UK continues to maintain strong science-base, and high animal welfare standards, in line with the requirements of the 1986 Act."
Northern Ireland's figures are published separately to the rest of the United Kingdom. They are a small fraction of the overall total, representing a few thousand animals.
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