The fourth in our series of interviews with potential candidates for next year's Mayoral election. Previously: Victoria Borwick (Tory), Andrew Boff (Tory) and Warwick Lightfoot (Tory).

Sian Berry is the Green's candidate for next year's elections. Unlike the Tory rivals we've previously interviewed, she is a strong supporter of the congestion charge. She's the only person we've ever known to use the words 'The North London Line is good'. And she's also got a thing or two to say about sash windows. Tell us why we should vote for you Ms Berry.

Why do you think you should be Mayor and what policies would you bring to the office that would make you stand out against anyone else who wants to be?
London has every advantage in its people, skills, language and location, but we?re also one of the most vulnerable cities to climate change so we have to be the city that sets the standard for the rest of the world on green issues. What better way than with a Green Mayor?

Real Green policies aren?t expensive, and don?t mean putting ?eco taxes? on everything and then giving the money away in tax breaks for the already rich. Many people in London are struggling just to find affordable housing and pay the bills every month.

I would help ordinary Londoners to save money on their bills by giving them free insulation; we?d improve public transport and make it cheaper for everyone; I would insist on proper affordable housing in every new development, not just small flats but real family homes; and I?d protect local shops and services and give small businesses a real chance on our high streets.

I?d bring with me my record of influencing policies at a London level, including pushing for the new emissions-based Congestion Charge through the Alliance Against Urban 4x4s. Backing me up I?d have the solid record of the Greens on the London Assembly, who have had a wide range of excellent policies adopted for London, thanks to their casting vote over the Mayor?s budget for the past four years.

In comparison with us, the LibDems and Tories have done nothing to help London since the GLA was created and they pose no challenge to Livingstone. A strong Green vote, with more Assembly members and me in the Mayor?s office would really make a difference to London.

Where do you live in London and what do you like best about it?
I live in Kentish Town, and think it?s almost perfect. The best thing is we still have a good high street that includes plenty of useful independent shops: a great butchers and fishmongers, several independent supermarkets, a bookshop and even a lovely ancient clothes shop that sells ?coats and gowns? to a clientele who must all look like my gran. Another good thing is the good transport links we have, and being near enough to Hampstead Heath to spend time up there without having to pay astronomic rents.

How do you yourself travel around London?
I mainly take the bus or tube, but I?m within walking distance of the Green Party?s office and also cycle to South Ken for work sometimes. I try to vary how I travel to keep it interesting. The North London line is good for going a long way east or west. I?m really glad that?s coming into Transport for London?s control soon; Londoners need to have more power over our transport, not more privatisation. The tube PPP has been a disaster.

What is your policy regarding irritant noise from mobile phone music players on the tube and buses?
Schoolkids on buses are incredibly loud sometimes, it?s true, but I think it?s impossible not to be annoying to other people, in some way or other when you?re a teenager. I?m sure they will get bored with the terrible quality of the speakers on their phones eventually.

Would you have introduced the Congestion Charge and if not will you repeal it?
I would definitely have introduced the Congestion Charge. Greens had faith in it all along, and all the scare stories put out by the other parties about 'rat runs' around the edge of the zone were completely unfounded in the end. The Western extension has similarly been a success in reducing traffic levels, contrary to what the Tories and LibDems predicted. We need more zones to help bring these benefits other parts of London now.

This is such an important point: cutting car journeys brings so much good to our city that the cuts in climate emissions that come with these policies start to look like a bonus. Air quality needs urgent action and, as Mayor I?d prioritise cleaning up our vehicle fleet (including buses, taxis and lorries) as well as cutting the need to use cars. More regular, cleaner buses, less traffic and more pedestrianised areas all over the city would do a lot to make London?s streets a more human place, rather than a hazardous car park full of fumes.

Do you support the building of a new runway at Heathrow and how would you reduce your own international travel if you become Mayor?
I was at the recent Camp for Climate Action and saw the villages that would be destroyed and met some of the people who would lose their homes if the runway was built. Aircraft noise affects all of us, even up in the north of the city, but the people around Heathrow suffer the most.

There?s no need for a new runway or any more flights than we already take, and expanding airports is utter madness given our urgent need to act to reduce climate change. Everything else the government tries to do looks pointless when they are intent on building new roads and runways.

What we really need to do is bring in fair policies like carbon allowances, which share carbon emissions out more equally - and these allowances should apply to Mayors too. Currently three quarters of flights are taken by 10% of the population ? encouraging more runways will only make this worse.

What would be your vision for the city by 2020 and how would you achieve it as Mayor?
My vision of a greener London is a place where daily life is less of a struggle for everyone, with affordable homes, locally generated energy, locally grown food, and with healthy high streets and workshops providing sustainable jobs in a more self-reliant economy - not one that depends only on the volatile international financial markets.

Do you have any London-based trivia our readers may not know?
London has hundreds of thousands of homes with sash windows, designed to open at the top and the bottom, but travelling around I can see that hardly anyone uses them properly.

Those Victorians were clever, and put in these windows because they can air and cool a room without artificial fans and air conditioning. With an equal sized gap at the top and bottom, the window creates a cycle of air that really does cool down your rooms ? try it tomorrow.

Have you ever been sick on the tube?
Only once, a long time ago. It wasn?t very spectacular, or an experience I?d like to repeat!

Coming soon...the Lib Dem candidates speak. And will we get Boris?

Image from the Green Party's website.

By 'Race4CityHall'