One of the clearest lessons from the history of nuclear energy is that government, industry and science work best when they work together. A scientific adviser must speak truth to democratic power without fear. In my view, it makes sense if democratic power then listens. It is in that spirit that I want to take an open and honest look at the history of nuclear power in Britain. If we are to retain public support for nuclear as a key part of our future energy mix, as I believe we should, then we have to show that we have learned the lessons from our past mistakes. And some of those mistakes were not small. Nuclear policy is a runner to be the most expensive failure of post-war British policy-making, and I am aware that this is a crowded and highly-contested field. We currently have around 6,900 cubic metres of high-level nuclear waste. That's about enough to fill three Olympic swimming pools. We have enough intermediate-level waste to fill a supertanker, and a lot more low-level waste. We manage the world's largest plutonium stocks -- more than a hundred tonnes -- and they will need guarding for as long as it takes us to convert it and build long-term deep storage. And if we don't, we will have to guard it for tens of thousands of years. Half of my department's budget goes in cleaning up this mess, and it will rise to two thirds next year. That is 2 billion