Questions were submitted via YouTube, txt and email from all over the world.

Mr Cameron...

• insisted that the UK had some of the strictest controls on arms sales in the world;
• attacked the Libyan regime's conduct as "unacceptable";
• explained the rationale for spending cuts, noting that the NHS - the service most important to vulnerable people - had had its budget ringfenced;
• argued that he was being tough-but-fair on banks;
• promised to rebalance the economy towards manufacturing and exports;
• re-link the UK to the fastest-growing economies in the world;
• committed to simplify the tax and regulatory system;
• said that cannabis was a dangerous drug connected to mental illnesses and that drug legalisation would only increase use and problems;
• noted that Iran was a different case from other potentially nuclear-armed states because it has vowed to wipe another state (Israel) off the face of the planet;
• promised UK troops would "come home" from Afghanistan as soon as that nation's own security forces were able to stop the nation becoming, again, a base for al-Qaeda or other terrorists;
• rejected the idea that an in/out referendum would resolve the question of EU membership and said he wanted to change the EU but remain a full member;
• defended the right of Wales and Scotland to continue to offer free tuition at universities but argued that fees will, for English universities, mean a better-funded, higher quality education in the years ahead;
• repeated his promise to reduce net immigration from the hundreds of thousands to the tens of thousands;
• said the Berlin Wall's fall in 1989 - "the year of liberation" - was the most important world event in his political development and continues to give him hope for the future;
• identified climate change as the greatest challenge facing the next generation and global poverty as the greatest challenge of today.

Barack Obama has been interviewed in this series.