The number of animals used in UK laboratories for scientific experiments has risen again.
Home Office figures show that in 2008, 3.7 million procedures using animals were carried out in England, Wales and Scotland - an increase of 14% on 2007.
This represents a spike in the year-on-year trend, although numbers have been increasing for several years.
More than three-quarters of procedures were carried out on rodents. Most of the remainder involved birds and fish.
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 experiments were for research and drug development; safety testing accounted for much of the rest.
Animal welfare groups have strongly criticised the increase, with the RSPCA calling the figures "disappointing".
But Lord Drayson, science and innovation minister, said the research was "critical to the development of new medicines and increasing the level of understanding of diseases".
The rise represents 454,000 more procedures undertaken in 2008, compared with 2007. An increase in the use of fish - used in 278,000 more procedures, or 85% more than 2007 - was a major contributor.
Zebrafish are particularly valuable in research because they can be genetically manipulated to mimic or "model" many diseases, and to have transparent bodies.
The number of procedures involving mice increased by 197,000 - an increase of 9% on the previous year. At the same time, the number of procedures involving rats decreased by 30,000.
Professor Paul Bolam, a neuroscientist from the University of Oxford, explained that researchers were increasingly moving from using rats to mice, because mice were relatively easier to modify.
"When we find out a particular disease is genetically driven, and when we identify the gene in humans (that is associated with the disease), we can find out what protein the gene codes for," he explained.
"So you can genetically modify (a mouse) to introduce this protein, and look at how that can lead to the pathology of the disease.
"I think that's leading to a big increase in the use of genetically modified mice."
'The three Rs'
In 2004, the government established a national centre called NC3Rs, which is dedicated to replacing, refining and reducing (the "three Rs") the use of animals in tests that are licensed under the Animals (Scientific Procedures) Act.
This latest increase in the statistics has caused critics to question whether policy-makers are failing to uphold this three Rs strategy.
But Dr Judy MacArthur Clark, chief inspector of the Home Office Animals (Scientific Procedures) Inspectorate, said the strategy was working, and that the numbers were more of a reflection of "an increase in fully ethically justified, high quality research taking place in the UK".
And according to the Department for Business, Innovation and Skills, the amount of publicly funded scientific research in the UK is increasing.
"Government investment through the UK science budget has more than doubled in real terms" from £1.3 billion in 1997/8, to £3.6 billion in 2008/9," the department said in a statement.
Simon Festing, executive director of Understanding Animal Research, said the three Rs were not just about reducing numbers.
"Improving animal welfare by refining procedures and replacing 'higher' animals with 'lower' animals are also important," he said.
"Using more animals does not mean more suffering. Many mice and fish are only used to breed better models of serious illnesses such as cancer or Alzheimer's, or to replace higher animals such as monkeys or dogs."
But use of non-human primates rose slightly, by 600 procedures - an increase of 16% on 2007.
This was caused by an increase in the use of old world primates, including macaques. The number of procedures using new world primates, found in Central and South America, decreased.
Dr David Reynolds, a senior scientist from Pfizer Global Research and Development, said this was driven by a move towards biologic medicines, which target specific proteins on human cells. Some of these were showing a lot of promise as cancer treatments, he added.
In order to adequately test the safety - these treatments have to be tested in a human-like model, and old world primates are closer relatives of humans than new world primates.
"In the short term, an increase in those projects is largely driving the increase in (the use of primates), said Dr Reynolds. "But, in the longer term, there are initiatives going on to reduce the number of primates used in research."
The Dr Hadwen Trust for Humane Research, a non-animal medical research charity, described the number of procedures as "shocking" and called on all major political parties to commit to "devising a roadmap to replacement".
The Home Office is currently taking part in negotiations for a recently proposed European directive - to align the regulation of animal testing throughout Europe.
Deputy Head of the RSPCA's research animal department, Penny Hawkins, said: "Replacing or avoiding animal use must be everybody's principal goal. In this respect, much more clearly needs to be done."