Everybody knows that when you want to win an argument, you need to ‘walk the talk’. Doing the opposite to what you preach tends to fatally undermine your case.
When that argument is persuading the rest of the world, in Paris, to tackle the root causes of climate change, your actions back home act as a global shop window.
But saying one thing, and doing another, is exactly the course this Tory government has taken over green issues. And they do it with no apparent embarrassment, or even understanding of the problem.
So we have the Foreign Secretary in the United Nations, and Cameron at the opening of COP21 in Paris making speeches that even Lib Dems would applaud. But what’s the track record back here in Britain where they drive the nitty-gritty of climate policy?
Take the Green Investment Bank. Set up by Vince Cable in 2012, a Lib Dem manifesto commitment in 2010, over its short existence it has successfully invested £2.3 billion into the UK’s green economy bringing in a further £7 billion in from the private sector. Not just that, its operations are already profitable. As a result the UK has more renewables, more combined heat and power plants, more energy efficient road lighting, more heat pumps. It has been a great Coalition success, down to Lib Dems in government.