On the stump: Darren Johnson

By BBC News Online's Dominic Casciani

Darren Johnson is looking rather pleased with himself. It's a sunny day and we are about to trot across Rainham Marsh on the north-eastern edge of the new Greater London Authority area.

But while the day's excursion is meat and drink to the Green Party's platform on bio-diversity, its mayoral candidate is beaming at the thought that frontrunner Ken Livingstone is telling supporters to vote for Green members of the assembly.

We want to drive a hard bargain. If we can make London a greener place in four years then we would have been a success

Darren Johnson

After months of suffering the fate of most small parties - low recognition factor - Darren Johnson is being talked about as a possible deputy mayor, or at the very least being made responsible for environment in a Livingstone cabinet.

While he currently lags on around 4% in the mayoral polls, Darren Johnson has a strong chance of entering the Greater London Assembly by virtue of the city-wide "top-up" voting system.

The Greens have grown in confidence during the election campaign and polls suggest that they may take two - possibly three - places in the 25-member assembly.

If Ken Livingstone wins, as all polls suggest, this small block may hold the balance of power for the independent mayor.

New London politics

For Darren Johnson this represents the next stage in a new model of politics which began when Jean Lambert won the party's first ever seat in the European Parliament last year.

"The biggest barrier that we have faced is that people don't like wasting their vote," he said.

Darren Johnson finds out he has Livingstone's backing

"Once we demonstrated that we can get elected, there has been a growing respect for what we stand for and more people are recognising that we need a green voice for London."

"I won't say that I'm a household name but compared to some months ago, people are recognising me."

So what exactly has been going on between him and the Livingstone camp?

"Ken has said that there's going to be a specific environment portfolio in his cabinet and he has said that he wants to see Greens elected.

"He needs to avoid a situation where Labour and the Tories form a two-thirds majority to block his budget. Having a strong Green group would help him."

That said, the candidate insists he has had "no discussions over the deputy mayor post" and that he will not lead a "Ken fan club".

"Ken is someone that we can do business with," he says. "We want to get stuck in with the decision-making process. I don't think you'll see me becoming a spokesman for Ken."

On the marshes

At Rainham Marsh, Darren Johnson is greeted by members of the area's conservation campaign who are battling against plans to sell off some of the site for industrial development.

Rainham Marsh: Loved by bird watchers

While hardly an oasis of calm - parts of the 11,000 acre marsh are surrounded by major roads - it is clearly a haven for wildlife.

Rainham Marsh, London's largest wetlands, is considered by the Royal Society for the Protection of Birds to be an area of national importance because of the sheer concentration of species that use the area around the year.

The birds nest and feed off the natural Thames lagoons. A high concentration of water mammals encourages larger birds such as kestrels to use the area.

It is areas such as these that the Greens say must be protected.

Elsewhere in the city, Johnson says, that battle has already been going on.

He cites the development of a massive leisure complex on Crystal Palace park in south London as an example of authorities failing to listen to the community.

"The community in Crystal Palace has fought hard against the development of the site but planning permission went through.

"I believe that we can use the office of the London mayor to exert as much influence as possible and support the community.

"Development of Rainham Marsh is one of the issues that I would be looking to call in and examine under the mayor's powers."

Policy platform

So after weeks of campaigning and talking to Londoners, what would Mayor Johnson's - or cabinet member Johnson's - priorities be?

The Green platform

Make London environmentally sustainable

Make London socially just

Make London more democratic

Make London work for its communities

"Clearly we are not going to be able to run a successful environmental strategy for London without working closely on transport," he says.

"We have got to make sure that there is a serious approach to environmental issues across the whole of the cabinet's responsibilities."

Mr Johnson identifies drawing up a bio-diversity plan, implementing an air quality strategy, waste management and a London-wide cycle network as among his key concerns.

But he stresses that congestion charging on the city's traffic has to be an absolute priority to reduce the daily jams in central London.

He quickly adds that if the proposed £5 daily charge doesn't reduce traffic, it should be raised until it does.

"There are green concerns across the whole of the GLA," he says. "You can have the best of both worlds. It is possible to protect open spaces and ensure that industry and jobs are protected too."

"One of the things that we want to do as a party is push through real benefits for local people.

The debate about the future of London is a debate about the future of the planet ... London can be a model for Green cities of the future

Green manifesto

"This has to mean more than just investment by companies coming into London. It means helping communities to create jobs for local people.

"One of our key policies is reducing the need for people to travel, ensuring that they have local services which will help regenerate communities.

"There are no reasons why you cannot have multiplex cinemas on the high street rather than out of town."

On the Greens' commitment to turning London into a "GM-Free Zone", a ban on genetically modified crops on London's small amount of agricultural land, he denies that its gesture politics, adding that it is something that people have to "take a real stand" over.

He also remains opposed to the building of a fifth terminal at Heathrow Airport and advocates restricting its night-time flights - something that is outside of the mayor's remit.

"We want to drive a hard bargain," he says. "If we can make London a greener place in four years then we would have been a success."