"Essential listening..." Why the US and UK went to war in Iraq and its legacy. Gordon Corera investigates.Twenty years ago a US-led coalition invaded Iraq to overthrow Saddam Hussein. The UK was America's main partner. For many it remains a war based on a lie. So why did it happen? Why was Washington so fixed on regime change in Iraq? And why did the British Prime Minister, Tony Blair, commit the UK to taking part? The BBC's security correspondent Gordon Corera seeks to find new answers to why the war happened and what it meant. Gordon speaks to those at the centre of the story, including some of the decision-makers and those living with the consequences. Tony Blair explains his thinking and why he promised to support George Bush. Sir Richard Dearlove, who was head of the UK's Secret Intelligence Service (also known as Mi6) at the time, defends the role of the intelligence services. The series also hears from the CIA's head of the Iraqi Operations Group, from weapons inspectors who were under pressure to find Saddam's WMD, and from Washington insiders. Gordon also speaks to Iraqis who experienced the "shock and awe" bombing campaign, the post-war instability and the arrival of ISIS. The series takes a fresh look at what really happened, revealing new information about the decision-making and the failures. And twenty years on, he explores some of the (ongoing) legacies of the invasion.