Above it, Bothwell wears another badge. It looks like a No Smoking sign, but with the lit cigarette replaced by a single, unusual word: Thimerosal. “It’s pronounced thigh-mare-o-sal,” says Bothwell, tapping the badge with her finger.

We are sitting in Bothwell’s half-decorated kitchen, the protective plastic wrapping barely off the state-of-the-art stainless steel appliances. Her nearly-posh English accent (she’s from Coventry, the daughter of a special forces captain-turned-software entrepreneur) seems rather out of place here in Long Beach, a lush, affluent Los Angeles suburb where huge mock-Tudor homes overlook a pristine golf course.

Bothwell’s effortless pronunciation of Thimerosal, a mercury-based preservative used in children’s vaccines, is the result of more than two years of study. During this time, Bothwell — the mother of three children, two of them autistic — has become an English Erin Brockovich, claiming a link between Thimerosal and her children’s disabilities and inspiring a legal crusade that has made national headlines in the US.

Indeed, the anti-Thimerosal chorus has reached such a crescendo that some predict it will become a key issue in the 2004 presidential campaign. It is already a subject of intense debate in California, where a study was released earlier this month showing that the number of autistic children in the state had doubled to more than 20,000 in four years. Ron Huff, the Californian psychologist who conducted the study, says: “I remember in the mid-1980s, when a child came in with autism, it was an event. You would get one or two in a year. I soon ended up getting one or two a month.

“I believed that every quarter the numbers would go down, but they just simply did not drop off. We’re now counting 800 new individuals with autism in California each quarter. And these are just the ‘classic’ cases; it doesn’t include the ones with difficult types of autism.”

Huff’s findings are not unique to California. All over America and in other countries, including Britain, the same autism epidemic is causing panic among parents. If Bothwell and her fellow campaigners can prove a link between Thimerosal and autism, Eli Lilly, the American pharmaceutical company that developed Thimerosal — along with several other drugs companies that manufactured the ingredient until the late 1990s — will be forced to pay billions in compensation.

Bothwell says this is not just opportunistic litigation by trial lawyers with big mortgages desperate to find the next Big Tobacco, and says she doesn’t want to put drug companies out of business: “They make things that help people.” But she accuses them of suspecting since the 1930s that the mercury in Thimerosal could poison children, bringing on autism in those with existing genetic weaknesses. The introduction of several new Thimerosal-containing vaccines in the 1980s, effectively doubling most children’s exposure to mercury, is the most likely reason why levels of autism began to spike at about the same time, Bothwell argues. Several thousand other plaintiffs across America agree with her.

Eli Lilly, unsurprisingly, does not share the view that they have been negligent, saying that the allegations are not based on scientific proof and that, besides, it has not made Thimerosal since 1974. Edward Sagebiel, a spokesman for the company, points out that the US Government took Thimerosal off the market in the late 1990s. “If the theory holds, wouldn’t you begin to see, from 2000, a decrease in the levels of autism?” he asks. The answer, according to Huff at least, is no: American doctors are still working their way through old stockpiles of Thimerosal vaccines. Also, it can take up to four years to come up with an autism diagnosis. However, Huff agrees that, ultimately, time will tell. “Because I’m a scientist, I don’t speculate until I’ve seen hard data,” he says. “There’s enough attention being given to Thimerosal that I think we’ll get a definite answer within five years.”

Bizarrely, Thimerosal remains virtually unknown among the general public in Britain, even though it is still used in DTP (diphtheria, tetanus and pertussis) jabs. British attention is still more focused on the infamous MMR (measles, mumps and rubella) vaccination, which has never contained Thimerosal.

BY RIGHTS, Claire Bothwell should be living the American dream, not fighting multinational pharmaceutical companies. She left England when she was 19, after marrying staff sergeant Ronald Miller of the US Air Force, who had been stationed at Upper Heyford, Oxfordshire.

The young couple moved to the former Wild West railroad town of Alamogordo, New Mexico, and made a down payment on a small two-bedroom family home. Bothwell says she remembers feeling giddy with excitement as she drove to the mall in her wood-panelled Ford Pinto station wagon and brought home groceries in stiff brown paper bags. Then one day in the spring of 1985 her husband went fishing near a New Mexico town called Truth or Consequences. He never came back.

Ron’s boat, it emerged, had capsized in choppy waters. A fisherman discovered his remains a month later. At the age of just 22, Bothwell was a widow. With encouragement from her father and friends, she decided to move to San Diego, California. She didn’t like it, so kept on driving in her Ryder van up Interstate 405 until she reached the southern suburbs of Los Angeles. Her journey came to an unscheduled end when she stopped at a petrol station in Long Beach. It was home.