Campaigners want graphic warnings like those on Canadian cigarettes

Researchers from the Cancer Research UK Centre for Tobacco Control Research have conducted a study into the effectiveness of using graphic images and warnings on cigarette packs.

They concluded health warnings had a shelf-life, and once they lost their impact they were ignored by smokers.

The only way to combat "warning fatigue" was to ensure messages were altered on a regular basis, they said.

The research, which was led by experts based at Strathclyde University in Glasgow, was conducted among smokers in seven countries.

It was commissioned by the European Commission to assess how best to continue with its drive to cut smoking rates across the European Union.

Future warnings will have to be reviewed and refreshed, maybe annually or every few years Professor Gerard Hastings

New style health warnings were introduced across the EU in January.

They must be printed in black on a white background and must cover at least 30% of the front and 40% of the back of a pack.

The NHS smoking helpline has reported an increase in calls since the warnings were introduced.

Professor Gerard Hastings, Director of the Centre for Tobacco Control Research, said: "Future warnings will have to be reviewed and refreshed, maybe annually or every few years.

"Otherwise we will fail to communicate the dangers of tobacco to smokers because of this 'warning fatigue'."

The research found the older style, smaller warnings had very little impact on smokers, who viewed them as simply pay lip service to the dangers of their habit.

But smokers thought the newer warnings were more credible and made more people consider the ill effects of smoking.

Graphic images

The research also found one of the best methods to boost the impact of the warnings would be to add graphic images of the effects of smoking.

The focus groups were shown a selection of graphic images used on Canadian cigarette packs.

These were very effective at attracting attention, but were less popular with smokers and made many feel defensive.

But the researchers suggest the images could be balanced by text giving people practical help, such as quit line phone numbers.

Researcher Elinor Devlin said: "This is a careful balancing act � there is a need to grab attention, but we want smokers to then interact with the warnings, not feel victimized."

Smokers who took part in the study suggested it would be a good idea to include more health information inside cigarette packs.