How should we combat ISIS?

Mark Mardell speaks to Jonathan Powell, Tony Blair's former Chief of Staff, lead negotatior during the Northern Ireland peace talks, and author of "Talking to Terrorists", Nick Witney, former chief executive of the European defence agency and senior Policy Fellow at the European Council on Foreign Relations and Haroon Moghul, an expert on Islamic history and a Fellow at the Institute for Social Policy and Understanding in Washington about how to combat the terrorist group.