Sean Duggan former group editor of our south-west London titles and a committed environmentalist who launched and ran our Green Guardian project across south London for five years.

Following Friday's eco-hustings, here are his thoughts on the mayoral race.

This year’s mayoral election is, in reality, a contest between two men (no surprise there then!)

In the blue corner we have Richmond Park MP Zac Goldsmith and in the red corner, Tooting’s MP Sadiq Khan.

Barring the unlikely prospect of them falling under one of London’s highly polluting diesel buses while on the campaign trail over the next two months, one of them will almost certainly be easing himself into Boris’s empty chair in City Hall come May 6.

From Monday: Who is London's greenest mayoral candidate? Eco-hustings grills Zac, Sadiq and co

However much Sian Berry for the Green Party, Caroline Pidgeon for the Lib Dems, or any of the other candidates pledge to do for the environment – and they have some really interesting ideas – the odds on them being in a position to deliver the goods are vanishingly small.

So, which of the two main contenders is promising to do the most to improve our environment?

The answer, at this point, is Mr Khan - and that really is a surprise, given that his opponent has been a high-profile environmentalist for most of his adult life.

Surely this is the golden opportunity which Mr Goldsmith has been waiting for to put his environmental principles into action across one of the world’s most important cities?

A city with an economy, and a population bigger than many countries.

And coming just months after the Paris climate change agreement, there has never been a more important time to have an environmentalist at the helm of this great city.

We need someone who will take decisive steps towards creating a low carbon economy in the capital – not lag behind as we are currently doing when compared to other parts of the UK let alone the greenest cities of Europe.

This is not only vital if we are to keep temperature rises well below 2oC and stop catastrophic climate change, but for the future of jobs and the economy of London.

Globally, green energy is already worth trillions and this city should be at the forefront of this new economic frontier which offers so many opportunities and so many jobs.

In a moving speech to delegates in Paris in December, David Cameron, said: "In London alone there’s five trillion of funds under management and we haven’t even really begun to generate the private finance that is possible to help in tackling climate change?"

Given the pressing need outlined by his leader, and given Mr Goldsmith’s long standing commitment to the environment, from being editor of the Ecologist to his threat to resign from the Government if it backed a third runway at Heathrow, expectations were very high that he would be the man to convert all the hot air into hard action.

But checking his campaign website, Zac’s Action Plan for London, last week I was stunned to find no mention of climate change at all in his environmental manifesto.

In fact there are just three points; protecting the greenbelt, tackling air pollution through tougher regulations on HGVs, encouraging greener vehicles and cycling, and improving parks and creating more green space.

To say what he is currently offering Londoners is thin on the ground is an understatement. There is not even a pledge to continue fighting expansion at Heathrow.

It is very hard to understand why he appears to be so unambitious. At Kingston Environment Centre last week people were perplexed and deeply disappointed.

It may be that he feels confident that his green record speaks for itself, allowing him to concentrate on campaigning on other issues such as the capital’s housing crisis. But if that is the case then he may be sorely mistaken.

When I interviewed people in his own constituency of Richmond last month for Kingston Green Radio a number had no knowledge whatsoever of his environmental credentials.

Outside the hustings on Friday two young women wearing bright blue support Zac sweatshirts were handing out flyers.

But instead of explaining the amazing things he plans to do for the environment, one side simply listed his environmental credentials to date and the other attacked Sadiq Khan, claiming his record on green issues has been entirely negative.

While the candidates’ past records are of course relevant, what Londoners primarily need to know from candidates is what they pledge to do in return for us putting a cross by their name on May 5.

And on that front Mr Goldsmith’s current green programme for London falls well short of what his rivals are promising.

Again and again at Friday’s environmental hustings, organised by the Green Alliance, he appeared on the back foot, while other candidates put forward more radical and exciting proposals.

Supporting Government policies, such as cutting subsidies on solar power and Boris’ decision to spend tens of millions of public money on a green bridge at a time when councils desperately need financial help to protect their green spaces, also didn’t endear him to the environmentally-aware audience.

His current position seems to be as a slightly souped-up version of Boris Johnson.

But, despite promising in an interview with this organisation prior to being elected that he “would be the greenest mayor ever”, Boris’s environmental achievements after two terms in office pale by comparison to the bold measures introduced by his Labour predecessor Ken Livingstone – from the congestion charging zone to the bike hire scheme wrongly dubbed Boris’s bikes.

London now needs a step change in the pace of change and that is something Mr Khan, despite having few environmental battle honours so far, really seems to have grasped.

His campaign website commits him to oppose fracking, oppose the third runway, expand the ultra low emission zone to arterial routes into London and it begins by saying: “London has the potential to be at the leading edge of the fight against climate change.

"It’s the right thing to do for our planet, for our health, and for the long-term future of our economy.”

Cynics might suggest that he is just trying to steal Mr Goldsmith’s thunder. But his interest in the environment dates back at least a decade.

When I launched the Green Guardian campaign across south west London in 2005 he was the only MP to attend the final awards night.

To be fair to Mr Goldsmith he wasn’t an MP then and went on win an award himself a few years later as Richmond’s Green Champion.

Mr Khan has clearly grasped the fact that in addition to the looming threat posed to all of us by global warming, the environment is central to everyone’s life in London today.

It is about not breathing poisoned air, about an effective transport network, about renewable energy at a reasonable cost, and it is about economic prosperity and green jobs, lots of green jobs.

The fact that he is prepared to pick up on sensible policy ideas from the Greens, such as setting up an energy company for London, is all to his credit.

Mr Khan, is surely right when he said at the Green Alliance’s event on Friday that London now needs someone determined to drive the environmental agenda forward: “You have got to be ambitious, and dare I say it Zac, radical.”

No doubt the difficult realities of life in City Hall mean mayors cannot always fulfill their ambitions. But if you don’t aim high to start with you simply won’t make the progress London needs and deserves over the next four years.

Agree? Disagree? Which candidate do you think offers the best green policies? Leave a comment below or email with a short letter for publication.