In one of the most controversial episodes of 'The Troubles' in Northern Ireland, UK soldiers fired on unarmed Catholic protesters, killing 13 in January 1972. We look at why British troops were there, what happened on that day, and how it further polarised Protestant Unionist and Catholic Republican communities. Successive UK governments insisted the soldiers had returned fire in self defence, until a public inquiry reported in 2010 that the soldiers had in fact fired first - and at fleeing, unarmed, protesters. The then Prime Minister, David Cameron, apologised on behalf of the government. We'll speak to former BBC Northern Ireland Editor, Eimear O'Callaghan, who as a teenager kept a diary of life in sectarian Belfast in the 1970s, later published into a book, and who reported for years on the struggle for peace.

Photo: A British soldier grabs hold of a protester by the hair. (Credit: AFP/Getty Images)