Authors of report into the effect of graphic pictures on teen smokers said they needed to be put in a more obvious place on the packet.
However, The Centre for Tobacco Control Research at the University of Stirling, warned pictures were not effective on regular smokers and only deterred teenagers experimenting.
As warnings need to be salient to be effective, positioning pictorial warnings only on the less visible reverse panel limits their impact.
They said the fact the UK has used the same pictures since 2008 may also have increased the "wear out" factor, particularly for regular smokers.
Positioning pictorial warnings only on the back of packs may have had a deterrent effect on never and experimental smokers, but for most measures no significant differences were observed.
The impact on regular smokers was negligible.
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