The milkshakes, which also contain chocolates, sweets, cake, cream and sauce, were found to have more than half of the daily recommended amount of calories for an adult.
Action for sugar, which is made up of specialists concerned with sugar and its effects on health, surveyed milkshakes sold in restaurants and fast food shops in the UK.
It has called for mandatory traffic light-coloured nutrition labelling across all menus.
Of the 46 of the products included in the survey, all would receive a red label for excessive levels of sugar per serving.
The government is already consulting on menu calorie labelling.
Public Health England (PHE) also has a sugar reduction programme as part of the government’s childhood obesity plan. It is challenging businesses to cut sugar by 20% by 2020 and milkshakes are included in that.