In 1993, McDonald's demanded an apology from Steel and four other members of London Greenpeace for allegations contained in a widely distributed leaflet that made minced meat of McDonald's. "I thought I should apologise to them," says Steel. Instead, between June 1994 and December 1996, she and Dave Morris, a former postman who had also refused to say how sorry he was rose to the challenge of fighting McDonald"s libel litigation.

They hunted down expert witnesses to talk about cows and milkshake containers, about rainforests and slaughterhouses. They cross examined McDonald's and were cross-examined by them.

Today, caught in limbo between the end of the trial and the imminent verdict, Steel sits in her poky, cluttered front room in Tottenham with a potential £5 million in damages and between £80,000 and £120,000 in costs hanging over her head and says: "I think we'll win. If we don't they'll probably declare us bankrupt and we'll get sent to jail if we ever criticise McDonald's again."

Would she do it? Would she take McDonald's to task again? Would she risk being deprived of liberty for the sake of further informing the public that she believes McDonald's pay their workers poorly, that their hamburgers are full of fat and that their packaging is wasteful? "You have to stand up for what you believe in," she says. Steel has a will of iron. A new book, McLibel Burger Culture on Trial by John Vidal, gives an account of the background to the 18,000 pages of court transcripts, 40,000 pages of documents and witness statements, and the 28 pre-trial hearings, and details highlights from the colossal court case. What it doesn't do is delve into the psychology of a young woman (Steel is 31) who is prepared to dedicate four years of her life to proving that McDonald's is a reprehensible outfit, which would prefer to spend eight hours a day in court rather than apologies for the sake of a quiet life, and the other 16 drowning in legal documentation. "Yes, the case has taken over my life, my house."

There has been no time for a social life. No time for boyfriends or a career. She worked at night behind a bar twice a week through the case. It was the only work that fitted in with her court attendance. Floor to ceiling, wale to wall, there are blue files containing transcripts of the trial. Plaintiffs statements. Witness statements. There are so many documents the: Steel is unhappy about the waste of paper. There is the research material ... a fat file entitled "Extracts from McDonald's Operation and Training Manual" and "Nutritional Aspects of Cardiovascular Disease".

Why did Steel ever get involved? "Because it was a unique opportunity to expose the inner workings of a multinational company. Because I believe in standing up for what is right. Because McDonald's shouldn't be pushing junk food. Because, beause, because ..."

I buy it. All of it. But there has to be more. The trial has been over for five months. Steel says she feels great relief at not having to attend court every day and prepare papers every night but she looks shattered. The strain is still stamped on the pointed features. The shadows under the darting bright blue eyes are still heavy. Her skin still looks grey. "Yes, it did affect my health," she says. "I got bad eczema and insomnia. And sure, I would rather have been climbing a mountain, walking by the sea or working on an allotment."

So why didn't she? "Because I relieve in a more just, caring society. A society where huge corporations don't have powers over us. A society vhere we share our resources."

There is a pause then Steel starts again about McDonald's, about the animals killed and the environmental damage caused. And Steel is true to her beliefs. In the bathroom is a massive bucket overflowing with empty plastic bottles destined for the nearest recycling plant.

She is a woman who fights for causes. The fact that the anti-McDonald's campaign was one of them and that this was the cause that involved her in a staggering legal battle was pure]y coincidental. It could just as easily have been London Greenpeace's campaign against the World Bank or the International Monetary Fund. It might have been a fight against any other fast food chain. Fighting for causes is just what Steel does. "I just have a gut feeling that oppression and injustice is wrong."

But she must have got something out of it herself. What about being the focus of media attention? What about the adrenalin that must have accompanied the agony of preparing for the cause? Wasn't it exciting?

Steel shifts position on the edge of the sofa. "Well, there was one part," she says. "We were trying to prove that McDonald's imported beef from Latin America to make their burgers. They said they had a policy of using British beef, but by mistake their solicitor handed over a document that referred to five consignments of beef from Brazil. I was sitting here, right here on this floor." Her sallow complexion suddenly flushes with excitement. "When I found it, I said: 'Yes, yes, 80 tonnes of beef, 80 tonnes ... and I phoned Dave and said, 'Have you seen it, have you seen it? Eighty tonnes of beef.'

"The other side asked for the document back when they realised their mistake but I had already checked the point of law and I knew that we were entitled to use the document as evidence."

Steel talks in legal jargon these days. Discovery of documents. Perhaps the Herculean feat of defending herself against McDonald's heavyweight team of solicitors and counsel has enticed her to leave her job behind a bar and train as a lawyer. She laughs. The legal world is much too wrapped up in power for her. Anyway, if she does win she will be too busy fighting for a more caring world where communities control their own destiny and if she loses she will be far too busy taking McDonald's to the European Court of Justice.

McLibel: Burger Culture on Trial, by Jobn Vidal, published by Macmillan, £15.99.