The mice will be kept as frozen embryos and will be created from embryonic stem cells that have been deliberately mutated to eliminate disease genes that scientists want to study.

Removing certain genes from a mouse embryo and allowing it to develop normally allows scientists to study the effects of having a defective gene on health and subsequent development.

Laboratory mice that have a gene deliberately removed have been used for more than 15 years as animal models of human diseases, but now scientists intend to make the work more systematic.

"Mice are pivotal tools for looking at the relation between genes and disease," said Professor Steve Brown of the Medical Research Council's Mammalian Genetics Unit at Harwell in Oxfordshire.

"There are several major international projects about to begin, one in Europe and one in the US, to knock out every gene in the mouse genome to see what is the consequence of the disease in the mouse and obviously translate that into the human genome," Professor Brown said.

Creating genetically modified mice for medical research is the main reason why the number of animals used in scientific experiments has continued to rise in recent years because of the valuable insights they give in understanding human diseases, he said.

Now the European Commission has agreed to spend €13m (£9.3m) on creating a library of frozen mouse mutants which should be available to researchers around the world by 2009.

"The focus of this project is to make mutations in almost all of the genes of the mouse genome. The target is about 20,000 genes, so we won't be doing all 25,000 mouse genes," Professor Brown said.

"The timescale for making this resource available is about four years from now. The project is due to start early next year and it has a timescale of about three years," he said.

It will take between 50 and 100 mice to resurrect just one mutant mouse strain with the desired traits. "I think the numbers of genetically modified mice will continue to increase," Professor Brown said.

"All these mutants will be stored as embryos. Researchers from around the world will be able to call up our repository and order a particular batch of stem cells from which they can create a mutant mouse," he said.

Professor Elizabeth Fisher, a neuroscientist at University College London, said that having a full library of knock-out mice will be an invaluable aid to understanding complex human disorders such as motor neurone disease.

"It saves me a lot of time, it saves me a lot of money. I wouldn't as an individual laboratory head necessarily have access to the expertise to produce those knock-out stem cells myself, so it is literally like going to a library and pulling out something useful," she said.