The UN provides great stimulus for debate. GCSE requirements to "explain, describe, narrate" and "argue and persuade" can be met via any number of UN case studies. A group could be asked to present a three-minute precis of the UN's history, or of the reasons for the US-led invasion of Iraq.
Another group could adopt roles in relation to the conflict - for example, a Sunni Iraqi angry at US aggression, or a Kurdish dissident who lost relatives under the old regime, or a diplomat who feels that the UN has been undermined. The views of these characters could be condensed into 250-word statements for students to discuss. It is an ideal way to demonstrate synthesis - a key requirement for higher grades in this mode of speaking and listening.