Scientists have created the first human-pig hybrids in a breakthrough which could pave the way for doctors to grow an unlimited supply of organs for transplants.

Britain is currently facing a crisis in organ donation because the number of deceased donors is dropping as advances in medical care mean more lives are saved.

In the past scientists thought they might be able to use the organs of pigs, which are roughly the same size of those of humans, but could not prevent the immune system rejecting animal tissue.

An alternative idea was to use stem cells - which can become any cell in the body - and simply grow new organs in the lab. But scientists have struggled to coax stem cells into complex three-dimensional structures.

Now a team at the Salk Institute for Biological Studies in the US has combined both concepts and shown it is possible to grow human tissue within a pig. The achievement took four years, 1,500 pig embryos and the stem cells from 40 people.