Question: What are the big issues that you're talking about?

Berry: My campaign is based around the fact that building a greener London also makes for a more affordable London, so I've got a range of policies including putting in a higher target for affordable housing in new developments, I've got plans to make public transport cheaper, as well as better, I've got plans to make sure that a living wage is paid to all public employees and to name and shame all private employers that aren't dealing with that problem as well.

I'm going to give free insulation to every home. At the moment, the Greens on the London Assembly have got a casting vote over the mayor's budget every year which is very helpful, and it means we've got a scheme where free insulation is available to anyone on certain benefits and to pensioners.

Basically I think that's a good scheme but it's not dealing with the problem fast enough, we've got some of the worst insulated homes in the country and we've got 1-in-20 families living in fuel poverty.

So to speed that up I'm going to make the scheme available to absolutely everybody for nothing, because I think everybody needs to get insulation eventually and I think giving it away for free is a very good way of making sure we don't miss opportunities to put it in.

So if somebody is moving house, if they're having other work done, the scaffolding is going up anyway, our people can go in and go 'oh by the way, we'll pay for this house to be insulated at the same time'.

That means there will be no disincentives and it will make sure that everybody sorts out insulation. We stop fuel poverty and cut our carbon emissions at the same time, so it's got a duel benefit for me as a Green.

The other thing with a universal scheme is you get better take-up among the people who are entitled to the other scheme as well. The fact that there is a great long list of conditions means that people on benefits who are pensioners might not think they're entitled even when they are, or they don't want to go through the rigmarole, or they're just worried about filling in forms.

Green councillors in Kirklees in Yorkshire have piloted this: they've brought it in for, I think, 30,000 homes over the next three years, paid for partly by the council, partly by the energy companies themselves because they're obliged to pay for this kind of thing.

They've got a universal scheme and it's working a treat, and the energy companies love it because they get really good value out of the money they have to pay to help energy efficiency, they can just walk down the street and every house is a potential customer, whereas with the other schemes, there are all kinds of reasons why they wouldn't knock on every door. So it just makes the whole thing very simple, and very effective.

Question: Are you consciously trying to change your campaign from your predecessor's, with a move away from focusing on just green issues?

Berry: It's trying to get across the fact that these two things go hand in hand. In the interim period since the last election we talked largely about improving people's quality of life, and that is true, we will improve people's quality of life with our policies.

But the very word quality is summing up something of what the other parties have done as a disservice for the green cause, which is make it synonymous with taxes, make it synonymous with expense, make it sound like a luxury add-one. All the stuff about 'can we afford to be green?', well we can't afford not to be.

That's what I'm trying to get across with this policy, this theme. These are all policies we'd do anyway - there's massive carbon savings to be made from everything we're doing, if we get more people on public transport for example - but stressing the fact that they're going to save you money is a way we hope of getting across that it's not all about green taxes.

Question: It's a fact that you're a lesser known candidate in a very high profile field this time, and you're up against some extremely experienced politicians. How are you going to make any headway?

Berry: I think eventually people will get very bored with the Boris and Ken show, and I think I will at some point become 'oh look there's this other fantastic candidate and she's got serious policies and she's not what you might expect, she's not saying what you might expect of a Green'.

I think all of those things are good plus points for our campaign. We are making inroads; we are one of the most powerful parties on the London Assembly simply because our two assembly members have this casting vote.

I think it's very important that I am included in this election because those two Assembly members have had power over London, they've made changes and I think they need to be held accountable for those changes. Obviously the media only focuses on the mayoral election, which I think is why it's important that I'm included in the hustings and in the profiles.

Question: Second preferences play a big part in the mayoral election, how do you decide whether to campaign for people's first or second votes?

Berry: It drives me mad - the while point of a two-round STV system is that the second votes decide who the mayor is. The first vote is your own, you can do what you like with it. There was a poll recently of opinion formers in London, high up, important people that the Evening Standard had hand picked, and even they were mainly planning not to put me as their first choice, but loads of them - 28 per cent - were putting me as their second choice, and that's not the way to do it.

The run-off is going to be on the second choice votes, that's where you put an insurance vote if you're worried about Boris getting in, if you really want to get rid of Ken, then you decide who your two front-runners are going to be and you choose whichever one of them will achieve what you want to do.

Your first vote is your own choice, it should be you vote for what you believe in, so I'm on the look-out for every first choice vote I can get. I'm going to try and educate people about this system because most of the second choice votes go to waste, because they're not cast for the people in the final round.

People need to make sure their second-choice vote is for someone they think is going to be in the final round or it just won't count for anything.

Question: Environmentalists like Jonathan Porritt have talked about Ken Livingstone as a mainstream politician who is committed to green issues, is it hard to campaign against him when his views are probably closest to your own?

Berry: We've been pushing him for four years on this and we know exactly where the points of difference are. Our Assembly members negotiate with him every year on a wide range of issues, not just green issues, they're the one responsible for the Living Wage Unit in London.

But yes, we know exactly how far we would go if we had control and we had a Green mayor. When we've got Ken Livingstone who is a Labour mayor, we push him as far as he can go but there is a limit to that. We know exactly how green he is and how much greener we could make things.

Question: And how green is Boris Johnson?

Berry: Well he rides a bike and I think that's about where it stops to be honest, I don't think he has a green bone in his body. He was with me in this advert that Greenpeace put out where we got together all mayoral candidates and said we oppose Heathrow expansion, and then about a week later he comes up with this plan to build a whole new airport to the east of London.

So he's not green, he thinks that airports can be expanded and that we can solve climate change at the same time, and that's utter, utter rubbish. Apart from all the health problems that another airport would cause or another runway at Heathrow, it would absolutely ruin all climate change credentials London ever had.

I'm sure he will at some point come up with something to say he's green but it won't wash and I don't think we can trust him to bring it in if he gets in.

Question: What do you make of the mudslinging between the two main candidates?

Berry: I'm staying out of it, because it is mud, that's what they're slinging about, it's not important issues they're arguing about. So I think I'd rather not comment on all of that and just stay out of it, I think there are more important things to worry about.

Question: Do you think the mayor's office is too powerful?

Berry: The office itself, yes definitely. The Assembly doesn't even have as much power as a local council, it doesn't have the ability to call in or delay mayoral decisions, it can't initiate policy on its own, and those things I think should change.

There should be policies that are able to come out of the Assembly; the Assembly should have a more powerful scrutiny role over what the mayor does.

I think it is too powerful an office for anybody to cope with, especially over eight years, there are bound to be problems - the fact there are so few is probably a bit of a miracle - because it was set up to be a fiefdom, that's how it was designed by a Labour government.

Question: This is only the second election you've fought?

Berry: I've fought for council seats three times and done very well each time. But it's a first past the post system and you've got to actually win and it's very frustrating to come very close every time and not to be elected.

So I've got elections in my blood. I fought the parliamentary election in 2005 and was one of only about 24 greens to get our deposit back. I did OK given it wasn't a target seat, the next-door seat was a target seat and there we got the fourth highest vote in the country, so it was a good election.

Question: And how's this one feeling?

Berry: We're doing so much more than we have done in previous years, we've now got this experience of working on the budget every year, we've got a very detailed knowledge of London policy now and we've got Assembly members with eight years experience each, so I think we've got a very strong basis for making policy.

We've got credibility and we've got a more organised campaign than we ever have before and one that's better funded, so we're going to have a much more successful election than we've ever had before or I'll eat my hat.