Talent issue - the campaigner: Sian Berry

I first saw Sian Berry when she was picketing Chelsea FC dressed as a footballer's wife in a platinum wig and mini-skirt, carrying a sign that said "Your Range Rover Is So Over". I first spoke to her when she was sticking fake parking tickets on to SUVs clogging the streets of Kensington. "Your car has been ticketed for destabilising the planet's climate," they read. "Please stop."

Today, in the urgent fight against global warming, Berry stands at the meeting point between direct action and electoral politics. She made her name as a maestro of witty acts to alert people to the gambles we are taking with our environment, once sending two Bin Laden look-a-likes to No 10 with a fake canister of nuclear waste and a card that said: "Dear Tony, Thank you very much for the present of nuclear power".

Today, the 33-year-old Berry is the Green Party's principal female speaker, and their candidate for mayor of London. As a down-to-earth product of Middle England, she has the ability to explain how global warming is already endangering us in plain language that relates to people's lives. She has worked in call centres, as a taxi controller and as an IT consultant. "I am sure the Green Party was founded by two men with two large beards," she says with a smile. "But it is an outdated image."

When she debates the petrolheads from Top Gear, she floors them with sound science and withering gags. Sweaty male journalists tend to get distracted by her looks one dubbed her "environmental Viagra" but she smiles through it all. It's easy to become depressed disseminating information about the climate crisis, but Berry says firmly: "I've got a plan. Why get depressed? We've got a little window to act. But we haven't got long. It's time to get going."

Portrait by Immo Klink