Ever since the link between smoking and lung cancer was established more than 50 years ago, the tobacco industry has displayed extraordinary tenacity when it comes to denying the scientific evidence showing that smoking kills.

In 1952, British scientist Richard Doll, working with his mentor Professor Bradford Hill, compiled a seminal study published in the British Medical Journal that established a "real association between carcinoma of the lung and smoking".

Over the next few years and decades, the evidence became stronger, but just as soon as this evidence began to emerge, Big Tobacco quickly launched a damage-limitation exercise. As early as 1953, the tobacco industry sought to spread disinformation to counter medical evidence. Tobacco companies hired New York public relations company Hill & Knowlton to "get the industry out of this hole", as industry documents released four decades later as part of legal processes revealed.

"We have one essential job - which can be simply said: Stop public panic ... There is only one problem - confidence, and how to establish it; public assurance, and how to create it," one Hill & Knowlton paper said. "And, most important, how to free millions of Americans from the guilty fear that is going to arise deep in their biological depths - regardless of any pooh-poohing logic - every time they light a cigarette."

In Britain, British American Tobacco (BAT) even invented a secret code word for lung cancer that was to be used in its internal memos.

The "C" word was to be substituted by Zephyr. As one BAT memo written in 1957 stated: "As a result of several statistical surveys, the idea has arisen that there is a causal relationship between Zephyr and tobacco smoking, particularly cigarette smoking."

Throughout the 1960s and 1970s, tobacco companies were brazen in their denials despite the mounting scientific evidence linking smoking with a range of cancers.

"None of the things which have been found in tobacco smoke are at concentrations which can be considered harmful," said a 1976 Philip Morris document. "Anything can be considered harmful. Apple sauce is harmful if you get too much of it."

During the 1980s, behind closed doors, there were doubts about whether the denialist charade could be maintained much longer. "The company's position on causation is simply not believed by the overwhelming majority of independent observers, scientist and doctors," said one internal BAT document.

And then in the 1990s came another bombshell. Second-hand smoke inhaled by "passive smoking" was linked with ill-health and there were calls to introduce smoking bans.

In 1992, the US Environmental Protection Agency produced a report on "environmental tobacco smoke" and concluded that it is a cancer-causing substance. In Britain, a 1998 report of the Scientific Committee on Tobacco and Health stated: "Passive smoking is a cause of lung cancer and childhood respiratory disease. There is also evidence that passive smoking is a cause of ischaemic heart disease and cot death, middle-ear disease and asthmatic attacks in children."

Despite the evidence, tobacco companies refused to accept the conclusions. Philip Morris, the world's biggest cigarette company, began a campaign to undermine the scientific case against second-hand smoke, highlighting what it labelled "junk science".

Its strategy was best summed up in a letter written in 1993 by Ellen Merlo, senior vice-president of corporate affairs, to the chief executive. "It is our objective to prevent states and cities, as well as businesses, from passive-smoking bans," she wrote.

Many tobacco companies have accepted that smoking causes lung cancer, but refuse to admit that passive smoking can cause disease in non-smokers. But having lost the debate over smoke-free offices and public spaces, the industry is turning its sights against the possible introduction of plain packaging.

Their fight against these proposals is based on undermining scientific evidence that plain packaging can reduce the number of children and young adults who take up smoking. They seek to discredit the research, a tactic they have used for more than 50 years of scientific denialism.

- INDEPENDENT