Evidence that the tobacco industry used underhand tactics to protect its market has been strengthened by fresh research.

The British Medical Journal (BMJ) has published a series of research papers looking at different tactics used by tobacco companies to both encourage young people to take up the habit and prevent them stopping.

The journal is also publishing evidence that passive smoking affecting UK children has fallen sharply over recent decades, possibly as a result of health warnings to parents.

Earlier this week, tobacco firms were accused of a deliberate campaign to undermine the World Health Organisation (WHO) anti-smoking efforts.

The latest research claims that:

• Tobacco companies launched "Operation Berkshire" to counter scientific evidence linking smoking to disease
• Evidence from advertising agencies shows that ads were intended to increase consumption, rather than simply brand share, as claimed by the industry
• Tobacco firms encouraged firms marketing "candy cigarettes" to children by allowing the sweet firms to mimic cigarette packaging and labelling, and by suppressing unfavourable research linking candy cigarettes to an increased chance of smoking later

The author of the report into advertising tactics, Professor Gerard Hastings said: "It is appalling that the industry is targeting some of the most vulnerable people in our society, such as the young and the poor - to take up a habit which may kill them."

Many of the claims are supported by internal tobacco industry documents brought to light by recent major court action in the US.

Professor Stanton Glantz, from the Cardiovascular Research Institute at the University of California in San Francisco, in an BMJ editorial, called on British American Tobacco, one of the biggest tobacco firms, to finally throw open its records depository in Guildford.

He said: "Doing so will help public health end the man-made epidemic that British American Tobacco and the other tobacco companies are spreading into the developing world.

"It will force the truth out of the shadows and into the public eye."

'Excellent news'

The research into passive smoking looked at levels of cotinine - a product of nicotine found in the blood - in non-smoking children.

They discovered that cotinine levels had halved over a 10-year period, crediting this to the number of parents who have given up, and increasing numbers of no-smoking areas in public places.

Professor Martin Jarvis, who led the Imperial Cancer Research Fund research, said: "These results are very encouraging, as they show that these changes are having a positive effect on one of the groups we most need to protect from second hand smoke."

It is the second piece of smoking-related positive news this week.

Earlier, researchers revealed that lung cancer deaths had fallen by half in the course of two decades, due mainly to fewer people smoking.