Tony Blair has publicly defended animal testing and accused anti-vivisection extremists of stooping to "appalling" depths. His comments have been applauded by scientists, but criticised by animal rights campaigners.
Here, two people from each side give their views.
PROFESSOR CHRIS HIGGINS, DIRECTOR OF THE MEDICAL RESEARCH COUNCIL CLINICAL SCIENCES CENTRE
"I think it's really important to get such public support from the Prime Minister.
These people - scientists, researchers and so on - are doing fantastic work, and they have been scared to go to work. It's very important to get this support because you can't have fear and intimidation of people going about their work in medicine.
I think one of the most important things to understand is that we have very tight regulations on experiments undertaken on animals. They are only undertaken when there is no alternative, and they are made to minimize any suffering.
Animal testing is regulated by EU and British Law. The studies are done under very controlled conditions. The Home Office regulates it very tightly, it inspects animal houses for standards and hygiene and ensures studies are not done if there is an alternative.
The law requires numbers of animal experiments to ensure we have safe chemicals in the environment and safe medicines.
The vast majority of experiments are done on mice or rats and most people consider these to be pests and put down nasty poisons for them.
People who say we can use cells don't understand medicine. You have to test these cells on a whole body. Animals are always the end point.
Many medicines come from animals, such as insulin which originally came from cows, and herceptin, which was developed from animals.
It's a very straight forward and simple choice - if you want new medicines that are safe and effective we have to use animals.
I would rather a new medicine was tested on a rat than tested on my child.
Children's lives are more valuable than rats'."
ALISTAIR CURRIE, CAMPAIGN DIRECTOR FOR THE BRITISH UNION FOR THE ABOLITION OF VIVISECTION
"The prime minister is rightly taking a tough line on extremists, but he is not looking at the problems of animal testing.
He is mixing the two up. The fact is that the public overall are very confused about animal experimentation. They are in favour of medical progress but they are against the suffering of animals.
Before this government came to power, animal testing was going down. Now they are ignoring the fact that it is on the rise.
Essentially animal experimentation causes great suffering to millions of animals in the UK, but doesn't produce the benefits to humans.
The drugs which are used in the UK have been tested on animals but that doesn't mean they needed to be. This is a technology that is decades old.
We can use computer modelling, human tissue cells in the lab, and well-designed studies on human volunteers. All of these things will tell us what happens on humans, unlike animal studies - which don't.
There is a conservatism in government and science that says 'we should keep using the old methods'.
Ninety per cent of drugs that have been animal tested fail in human studies - they never actually make it onto the market, because they don't work.
So the government is backing a system that fails.
It is legal in this country to poison an animal to death, to inflict brain damage on it and surgically manipulate it. Mice given cancer are suffering severe pain and distress. Rats that are asphyxiated to death are suffering profoundly.
The animal is small but the suffering is great."