The revelation comes after the release of more than 800 cats and kittens from Hill Grove Farm, in Oxfordshire, which has closed due to its owner's retirement. It was the last place in Britain to breed cats for scientific research and testing.
However, the Independent on Sunday can reveal that dogs, mice, rats and pigs bred for vivi- section by private laboratories are still being killed without serving any scientific purpose.
The overbreeding is being kept secret because there is no legal requirement on labs to reveal how many animals they breed or cull.
The investigation, by the British Union for the Abolition of Vivisection (BUAV), found laboratories are breeding up to four times as many animals as they require.
Last year more than 6.5 million mice and around 2,400,000 rats were culled. And more than 1,000 laboratory dogs, an estimated 25 per cent, were killed because they were not needed. Most were bred for testing pharmaceuticals and spent their whole lives in kennels waiting to be experimented on.
Several million more rabbits, guinea pigs and monkeys are believed to die each year.
Sarah Kite, head of BUAV's research, said: "This waste of life is totally outrageous. Based on the information we have received we have found millions of mice, rats and dogs are being killed. There are probably many more that we don't know about. This is the hidden side of the research industry."
Only government-run laboratories, including the Ministry of Defence's Porton Down laboratory, publish figures for overbreeding. The Defence Evaluation Research Agency at Porton Down gives unused rats and mice it does not use to nearby bird sanctuaries for food.
Yesterday Matthew Taylor, the Liberal Democrat environment spokesman said laboratories had to be accountable, not just for the experiments they conduct but the conditions they kept animals in.
"The only answer to this is a body to oversee animal experimentation with real teeth," she said. "Labour has given the impression that they would introduce this before the last election but so far precious little has happened. I am shocked by these figures."
The Research Defence Society, which defends the use of vivisection for scientific research, said that the latest figures showed that around half of laboratory animals were not being used.
"Nobody is overbreeding animals deliberately because they are very expensive to breed and keep," a spokesman said. "The reason why more animals are bred than used is because in experiments you need animals of identical size and weight."
The excess animals have to be killed by approved methods including gassing, breaking their necks, blows to the head or administering excess doses of anaesthetic.
Last year an influential government body recommended that laboratories "minimise" the number of animals they cull.
The Animal Procedures Committee also recommended that breeding establishments and laboratories be forced to report to the Home Office how many animals are killed.
The Home Office said that it was currently "considering" making laboratories publish their figures.
But MPs said that ministers should take immediate action when they return to Parliament after the summer recess to reassure the public.
Geraint Davies MP, chair of the Labour back-bench environment committee, said: "The public has a right to know how many animals are being used for experimentation and needlessly killed.
"The Government needs to respond to people's sensitivity on this issue."Reuse content