UK scientists have developed genetically modified chickens capable of laying eggs containing proteins needed to make cancer-fighting drugs.

The breakthrough has been announced by the same research centre that created the cloned sheep, Dolly. The Roslin Institute, near Edinburgh, says it has produced five generations of birds that can produce useful levels of life-saving proteins in egg whites. The work could lead to a range of drugs that are cheaper and easier to make.

Professor Harry Griffin, director of the institute, told the BBC: “One of the characteristics of lots of medical treatments these days is that they’re very expensive.”

“The idea of producing the proteins involved in treatments in flocks of laying hens means they can produce in bulk, they can produce cheaply and indeed the raw material for this production system is quite literally chicken feed.”

Roslin has bred some 500 modified birds. Their existence is the result of more than 15 years' work by the lead scientist on the project, Dr Helen Sang. But it could be another five years before patient trials get the go-ahead and 10 years until a medicine is fully developed, the Roslin Institute cautioned.

Therapeutic proteins such as insulin have long been produced in bacteria; but there are some complex proteins that can only be made in the more sophisticated cells of larger organisms. Scientists have successfully made a range of these molecules in the milk of genetically modified sheep, goats, cows and rabbits.

The work at Roslin shows it is now possible to use chickens as “biofactories”, too.