The claimants argue that the cigarette companies failed to minimise the risk of disease by reducing nicotine and tar content of their products as soon as they knew their harmful and addictive effects.
Although the money granted yesterday will only cover preliminary preparation for their case, the potential implications for the tobacco industry are devastating.
About 110,000 people die prematurely each year in Britain from smoking-related illnesses like lung cancer and heart disease, and hundreds of thousands more suffering damaged health.
With so much at stake, the cigarette-makers are likely to delay and obstruct the action for years, and spend millions of pound opposing every claim. The defendants will be the five big tobacco producers in Britain - Imperial, Gallaghers, British and American, Philip Morris and Rothmans - who accept a statistical link with illnesses including heart and lung diseases, but not a causal link.
The Tobacco Manufacturers Association expressed "surprise" at the granting of legal aid yesterday.
The claimants will be able to make use of information thrown up by two potentially vast court cases recently begun in the United States. In one, several states are suing tobacco companies to try to recoup the costs of health care for victims of smoking-related illnesses. In the other, 50 law firms have joined forces to bring a combined action on behalf of all potential claimants.
Although there have been hundreds of cases brought already in the US, no one has won damages. One woman was successful in a lower court, but could not afford to continue after the case was contested to the Supreme Court.
The British claimants will spend the next 4-6 months collecting expert evidence on links between smoking and ill-health, and to show that cigarette companies could have reduced the health risks earlier by reducing the tar and nicotine content of their products. They will then take counsel's opinion, before sending their case to the Legal Aid Board asking for money to fund a full High Court case.
Yesterday's decision by the Legal Aid Board means the tobacco giants will be faced by a joint action with correspondingly greater resources rather than being able to take on the claimants one by one.
In the US, some 700 individuals have sued the tobacco companies. Not one has ultimately succeeded.
Outside the US there have been very few actions and no successes.
The smokers and the families of some who have died are alleging the tobacco industry owed a duty of care to its customers; that they failed to warn consumers about the risks and failed to minimise those risks.
They are also claiming that the duty of care is heightened in these cases because the great majority of smokers start the habit when they are children and do not have the ability to make judgements about health risks.
Charlie Hopkins, of Leigh Day and Co, one of the lawyers representing the claimants, said they already had documents from the US and from Britain showing how much the tobacco companies knew.
The claimants allege the industry was aware during the 1950s and 60s that nicotine was addictive, and that tar levels were the main factor contributing to the high health risks.
One of the claimants, John Ellner, 61, has been smoking for 50 years and still smokes 10 a day. He says the habit has left him struggling to breathe and unable to work. He says smoking has "ruined his life", but insists he cannot give up. His claim that he is addicted will form a key part of his case.Reuse content