Who is the most significant living figure in global politics, and why?

Well there is the most prominent one for sure, and that is Barack Obama, and not for the right reasons. I had great hopes for him when he was elected but these have gone entirely unfulfilled. He has acted, particularly on foreign policy, in exactly the ways of his predecessors. But for the most significant I'd go for Xi Jinping, the president of China.

The country has developed amazingly in the last two decades – I'd hazard unprecedentedly – but it is going to become the dominant superpower in my lifetime, I'm sure. Of course it has its internal problems, currently over Hong Kong, but the country under successive leaders, now Xi Jinping, has been transformed into an economic and cultural powerhouse. I'll certainly be trying to convince my youngest that he should study Chinese at school.

What makes a good idea great?  

Putting it into practice, surely. We all have them, lying in the bath or when we're daydreaming or looking for another way forward, but most of them disappear down the plughole. Only when the idea is persevered with and tested does it stand a chance of becoming great. There's that line from a Gershwin song, "They all laughed at Christopher Columbus when he said the world was round, they all laughed when Edison recorded sound". Great idea for a song, great ideas expressed. Pretty much says it all.