Tonight: Famine - Millions on the Brink

Rageh Omaar reports on a growing humanitarian crisis as 20 million people in South Sudan, Somalia, Nigeria and Yemen teeter on the brink of famine. As the UN says the famines are the worst the world has experienced since 1945, this programme looks at what can be done to prevent scenes similar to those in 2011 when over a quarter of a million people died of starvation.