One of Ollie Bray's Assemblies at Musselburgh Grammar school in East Lothian.

2. Question Can you change the world?

6. Small ideas change things

7. Question Do you like hot drinks? (Tea, coffee, hot chocolate)

10. If everybody did we could save enough electricity to run all the street lighting in the whole country. Apparently.

11. Question Do you have a mobile phone?

13. Your mobile phone charger is more powerful than it looks. And 95% of the energy used by the phone chargers in this country is wasted. They're only doing their job - i.e. charging phones - for 5% of the time.

14. Question Do you like to chew gum?

16. Here's something to chew on. In the UK, we spend about £150m every year cleaning chewing gum off the streets.

17. What could we do with that £150m ? Not much? Build 3 hospitals, maybe. Employ 8 and a half thousand teachers.