Medical scientists have taken an important step towards understanding how the diseased liver can repair itself in a breakthrough that could eventually lead to the development of new treatments for chronic liver illnesses, which at present can only be cured by organ transplants.

The researchers have worked out how to stimulate the production of vital liver cells known as hepatocytes which are lost when the liver is attacked by potentially fatal conditions such as cirrhosis or chronic hepatitis.

Liver disease is the fifth biggest killer in Britain and is the only major cause of death that has seen a continual year-on-year increase over the past 40 years – more than twice as many people die of liver disease now compared with 20 years ago.

About 16,000 people in the UK died last year of liver disease, and the number of people on the waiting list for organ transplants has increased from about 300 five years ago to nearly 500 now.

The latest research, published in the journal Nature Medicine, has unravelled the network of complex biochemical signals that trigger the regeneration of cells within the liver, the body's main organ for filtering harmful toxins from the bloodstream.

Although the human liver has remarkable powers of natural regeneration, this often results in the replacement of the wrong kind of liver cells. Instead of hepatocytes, the damaged liver tends to make to many bile duct cells, the scientists said.

The scientists were able to shift the balance towards making more hepatocytes by altering the expression of certain genes at the earliest stages of liver cell development. The discovery could lead to the development of drugs that perform the same function in patients, they said.

Luke Boulter of the Medical Research Council's Centre for Regenerative Medicine at Edinburgh University, and lead author of the study, said that understanding how new liver cells are regenerated is key to finding ways of repairing damaged liver tissue.

"This research helps us to know how to increase numbers of cells that are needed for healthy liver function and could pave the way to finding drugs that help liver repair," Dr Boulter said.

Professor Stuart Forbes, associate director of the Centre for Regenerative Medicine, said such studies are needed to tackle the increase in demand for liver transplants. "But the supply of donated organs is not keeping pace with the demand. If we can find ways to encourage the liver to heal itself then we could ease the pressure on waiting lists."

500: The number of people in the UK on the waiting list for organ transplants, up from