Placed on a scaffold made of biodegradable plastic, the grew and fused together to form discs of heart valve tissue just an inch wide. As the heart valves developed, the scaffold decayed, leaving behind solid tissue.

The researchers are due to begin testing the valves in animals this year and trials on people are expected to follow.

Professor Jeremy Pearson, of the British Heart Foundation, which funded the latest work, said: "Replacement human, animal and mechanical heart valves remain lifesaving for thousands every day in the UK.

"However, Professor Yacoub and his team are among the leaders in research to design better replacement heart valves using human stem cells and natural biological materials as the framework for these cells to grow in.

"We look forward to seeing the solutions to unresolved practical issues that will allow the promise of experimental research to become a reality for patients in the not too distant future."

Hearts have four valves which ensure blood flows in the right direction.

They have to be replaced if they leak or fail to open properly. Around 10,000 people a year need such surgery.

Adults are usually given artificial replacements, while children are given valves from human donors.

But donor valves are in short supply and tend to deteriorate over time, while patients given artificial valves must take drugs for the rest of their lives to stop blood clots forming.

Earlier this year, Israeli researchers said they had grown a tiny beating heart from stem cells from a newly-created embryo