Campaigners have called for a 20% sales tax on confectionery as well as a complete ban on price promotions in response to retailers making larger 'sharing packs' better value than smaller sizes.
Action on Sugar (AoS) said some chocolate confectionery sharing bags contained 29 teaspoons of sugar - four times an adult's maximum daily sugar intake.
However, more than one in five adults (22%) eat the sharing bags alone, in one go, with the figure rising to 35% among 16 to 24-year-olds, a survey for AoS found.
AoS said the removal of price promotions on high sugar products could cut almost two teaspoons on average from every individual's diet per day.
AoS chairman Professor Graham MacGregor, said: "It is shocking that food companies are being allowed to exploit consumers by manipulating them into purchasing larger size bags of chocolate confectionery on the cheap."