Green Party mayoral candidate Sian Berry said today she would work with Boris Johnson if he won - even though he would be "a disaster" for the environment.

Ms Berry said it would be better to work with the Tory than against him.

But she admitted her party would not have as much influence as it has done under Ken Livingstone, who relied on the Greens to get his budget through.

Ms Berry, who could win a London Assembly seat, has urged her backers to use their second preference votes for the Labour candidate.

However, she told the Evening Standard: "I'm sure Greens on the Assembly would be happy to offer advice [to Mr Johnson].

"But the danger with Boris Johnson is the way the constituencies are set up means they [the Tories] don't need anyone's votes to get their budget. We would talk to them but they wouldn't have to talk to us."

She added: "I saw very little in Boris's manifesto which was really getting to the heart of the matter. I saw a lot about trees, a lot about graffiti, that's the environment as far as Tories seem to be concerned. There's not the concrete measures to tackle the major carbon emissions in London."

Almost 60,000 voted Green at the last mayoral election. Ms Berry, 33, denied she was the green wing of the Labour Party, insisting: "We're getting more out of it than he [Mr Livingstone] is."

Since her endorsement, she appears to have been distancing herself from the Mayor, describing him as the "least worst" option on offer. "We've described a second preference vote for Ken as an insurance against Boris," she said. "We're not expressing massive endorsement of Ken or Labour in any way.

"You've got to look at who is likely to be in the final round and it's those two, so you've got to chose between them. Ken Livingstone would be less of a disaster than Boris Johnson."

Ms Berry insisted the Mayor had not made her a job offer to win her party's support. "We've not even slightly had a discussion about anything that might happen after the election," she said.

Fourth on the Greens' list, she would need an Assembly vote share of 13.5 per cent, which the party achieved at the last council elections, to win a seat. She said she would be the member "with the good ideas" to make London greener. Along with the other main candidates, she opposes Heathrow expansion. She would also close City airport.

"Most of the flights are short-haul for which there are alternatives, so I don't think it would be an enormous loss to the City," she said. "We definitely wouldn't let them expand. If they did hang in there the earliest chance we'd get is in about eight years when the leases on other parts of the land the GLA owns cannot be renewed and then it would actually have to close."

Ms Berry has only flown once in the last 10 years - for a holiday to Croatia in 2005 - and would try to cut the amount of travel involved in being Mayor.

"If you're just going to make a short speech is that better done by video? You've got to look at all those options," she said.

"There's time and money involved, as well as carbon emissions. On some occasions, yes, you would have to go to places that you can't reach but I think most of Europe is accessible by train."

Her flagship policy is to extend the Mayor's green homes scheme so free insulation would be available to all London households. "We have some of the worst insulated homes in the country," she said. She said her own environmental failings included printing off emails and smoking, which she pledged to give up if she became Mayor.

WHERE BERRY STANDS

PROTECTING GREEN SPACES

"It is impossible for Londoners to have a decent quality of life if the environment is polluted, noisy, poorly maintained and under threat locally and globally ... We need to be vigilant against pressures to turn everything outside zone 2 into a suburban sprawl. New developments should be on previously-used land only, with our green spaces preserved."

She also pledged to hold planning meetings in public, remove traffic from parks, promote "green roofs" and plant trees on every street.

£25 GAS-GUZZLER CHARGE

"I don't think you can bring punitive measures at the top end without bringing in incentives to switch to the bottom end. What you may find is that people go out and buy band-B cars and have their discount taken away after a year and people will feel cheated. I wouldn't extend the zone further.

The Low Emissions Zone is absolutely necessary - about 1,000 people a year die because of our poor air quality."

YOUTH CRIME:

"You've got young people getting involved in gangs because local councils have cut their funding for youth services. They have overcrowded homes so they have no choice but to be on the streets. But I think it's got to be down to them. Adults can't predict what young people like to do."

CITY FAT CATS

"For City employees who are on massive bonuses and own substantial amounts of property there is a ceiling on how much council tax you can pay. We ought to have different ways of raising money, either through business rates or local income tax. My main policy is to raise the wages of the lowest paid."

GREEN BUSINESS

"This is about future-proofing London's economy. At the moment we are relying completely on financial services and the washover like leisure and entertainment. We're totally reliant on fuel for transport. So when the economy changes, when financial services take a dive and fuel prices go up and up, London is going to be in trouble unless we have new industries ready."

KEY POLICIES

• Closing City Airport, no airport expansion, no Thames Gateway bridge

• 20p off all bus and off-peak Tube fares

• Free insulation available for all homes

• Living wage of £7.20 an hour

• Half of the space in new retail developments for local businesses

• Cheap loans for renewable energy generation

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