The importance to medical research of genetically modified (GM) mice was highlighted yesterday as official statistics showed that their use in scientific experiments has exploded over the past decade.

Almost all of the increase in animal testing since 2000 has resulted from the revolution in research that means biologists now routinely alter the genes of laboratory mice in order to mimic a range of human diseases, from Alzheimer's and Parkinson's diseases to cancer and cystic fibrosis. For the first time, the number of scientific experiments and other "procedures" involving lab animals that have been either genetically modified or afflicted with harmful genetic mutations has exceeded the number using normal animals. More than a million GM mice were created in Britain last year alone. Such tests have already enhanced our understanding of a range of human diseases, from cancer to Alzheimer's and the common cold.

The total number of scientific procedures involving animals fell by 1 per cent last year, Home Office figures showed yesterday, but there was a steady and significant rise in the use of GM mutants, which accounted for nearly 53 per cent of the 3.6 million procedures carried out in Britain.

Most of the increase resulted from using or breeding GM mice for medical research, in which human diseases can be mimicked in animals as a result of changes to their DNA. This allows scientists to study human disorders in more detail under controlled conditions, and to test drugs and other potential treatments on animals before trying them on people.

About 3.5 million animals were used in last year's 3.6 million procedures – about 1 per cent fewer than were used in 2008. However, the number is still the second highest for 20 years and reflects a continuing upward trend, due primarily to greater use of GM animals and those with harmful genetic mutants.

Breeding to produce GM animals, mostly laboratory mice, and others with genetic mutations rose by 10 per cent last year to 1.5 million procedures. For the first time, experiments with genetically "normal" animals accounted for less than half of the total – 48 per cent. There was a 9 per cent rise in scientific procedures involving mice.

Researchers say the ability to breed GM mice that mimic human diseases, or have other traits that would not exist naturally, has revolutionised our understanding of the fundamental biology of human disorders and led to many breakthroughs in treatments. However, those opposed to vivisection question the value of such work, arguing that it offers only limited benefits and causes more suffering for animals.

Gemma Buckland, a science and policy officer at Humane Society International, an animal rights charity, said it was troubling to see such a rise in the use of GM animals that often suffered organ damage, physical deformities and tumours. She said that despite "very bold claims" made about their medical application, the truth was that "GM technology is still merely an attempt to add or knock out a gene in a different species to make it a less crude surrogate for humans".

"In [most] cases, the animal doesn't bear the desired genetic mutation and is simply killed as surplus," Dr Buckland said. "Even when the genetic mutation is successful, the end result is still an unsatisfactory animal model."

Scientific procedures using cats, dogs, monkeys and horses – which have special protection under law – all fell last year, by 7 per cent in the case of monkeys, by 3 per cent among dogs and 24 per cent among cats. Procedures involving mice accounted for three-quarters of all animal tests, while those involving monkeys, cats, dogs and horses accounted for less than 1 per cent.

The Home Office minister Lynne Featherstone said the figures showed the important work done to regulate vivisection in Britain, which was widely regarded as having the world's toughest laws for the licensing and monitoring of animal research. "The Government is committed to continuing with the highest standards of animal protection. We are also committed to ending the testing of household products on animals and working to reduce the use of animals in scientific research," she said.

Under the Animals (Scientific Procedures) Act 1986, animals can be used in experiments only if there is a clear potential benefit to either people, animals or the environment, and when there is no means of obtaining these benefits without using animals.

Scientists must obtain Home Office licences to work on animals and the 190 establishments with such licences are subject to spot-checks by inspectors. Last year there were 40 infringements of the rules, most of which were self-reported and fell into category "A", the least serious. No infringements fell into the worst category "D", which would have led to prosecution.

How can 'Supermice' help?

Cancer

In the 1980s, Harvard scientists created OncoMouse, a GM mouse that was susceptible to cancer. It provided scientists with a useful animal "model" of a human disease that strikes one in three people at some time in their lives. Other GM mice that develop cancer have since been created.

Physical performance

In 2007, scientists developed a GM mouse with genes that affect glucose metabolism and the efficient use of body fat. The "supermouse" had extraordinary physical abilities comparable to the best human athletes, being able to run 4 miles for five hours without stopping.

Knock-out mice

Many GM mice used in medical research have had one or more of their genes deliberately disabled or removed. This targeted approach to creating GM mice allows scientists to mimic a range of human disorders known to be caused by a single defective gene.

Colour vision

Mice naturally see in blends of just two colours, while humans have trichromatic vision. In 2007, scientists created a GM mouse with three-colour vision by inserting a human gene for red colour vision into their genome. The research led to a better understanding of colour blindness in men.

Immune system