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.

In fact, sadly so successful that the Tories announced its privatisation. Which will undermine it entirely.

Step in the House of Lords.  The Enterprise Bill currently passing through the House is the Tories’ vehicle to take out all the green purposes of the bank, entrenched in the original act, before sell-off. Those purposes are the nation’s guarantee that the Green Investment Bank can’t just become a wide-ranging investment bank like any other.  The nation needs those guarantees to keep that vital momentum of green investment for our long term.

Our task as the Lib Dem group in the Lords was obvious and clear: to guarantee those green purposes through privatisation and ensure they stuck for the long term.  The challenge was to persuade the rest of the House that we could find a solution that worked.  That’s exactly what we did.

We introduced the mechanism of a special share in the Green Investment Bank held by ‘green guardians’ appointed initially by the Climate Change Committee.  Those green objectives could only be changed if the three green guardians agreed unanimously.

It was a great solution that met everybody’s needs.  But of course the Government resisted.  We called a vote and the House of Lords agreed our proposal by a majority of 46.  A Lib Dem victory for our green economy.

But the Green Investment Bank is only one of many steps backward for our environment here in the UK.  The solar and on-shore wind industries have been decimated.  The energy efficiency led Zero Carbon Homes programme has been binned.  Community energy projects have been made uneconomic.  Investor confidence in renewable energy has been squandered.  The Green Deal has gone.

So as we exhort fellow members of the world community to work with us in Paris to nail down that vital deal for all our futures, the real climate leadership we had under Chris Huhne and Ed Davey has evaporated.  Lib Dems in Parliament are working hard to turn the tide.

* Robin Teverson is a Liberal Democrat member of the House of Lords.