A new survey has found that the sugar found in high street iced coffee drinks is more than that found in a can of Coca-Cola or in a Mars bar.

The research was carried out by consumer group Which? which compared frappes and frappuccinos from Caffe Nero, Costa and Starbucks to find the amount of sugar in each.

Which? suggests that the sugar contents in these popular drinks are “exceptionally high” with a Starbucks frappuccino with semi-skimmed milk containing 48.5g of sugar, equivalent to 12 teaspoons.

This is despite NHS health advice saying that adults should consume a maximum of 30g of sugar per day (around seven teaspoons).

Sugar contents in Caffe Nero, Costa and Starbucks iced coffees revealed

Caffe Nero's Belgian chocolate and hazelnut frappe contained 44.5g of sugar (11 teaspoons) while Costa's chocolate fudge and hazelnut frappe with oat milk was found to contain 42.6g.

For comparison, a 51g Mars bar contains 31g of sugar while a can of Coca-Cola contains 35g of sugar.

Whilst the calorie contents of drinks must be displayed in stores, sugar contents do not, leaving many customers vulnerable to exceeding their maximum intake, warned the watchdog.

Dairy-based drinks derive some “locked in” sugar from lactose, but all the drinks also contained high amounts of “free sugars”, those that have been added and contained in syrups, honey and fruit juice.

Which? says Starbucks, Costa and Caffe Nero customers 'could unwittingly be consuming much more sugar than they realise'

Which? nutritionist Shefalee Loth said: “Our analysis of sugar content in iced coffee blends shows people could unwittingly be consuming much more sugar than they realise, with potentially damaging implications for their health.

“High street chains need to take more responsibility and reduce the excessive sugar content of some of their drinks to protect people’s health.

“When buying an iced drink, there are alternative, healthier options to choose from, such as a standard iced coffee, which contains far less sugar.”

Starbucks, Costa and Caffe Nero customers speak out after 'exceptionally high' sugar contents in drinks revealed

A Starbucks spokeswoman said: “We are committed to helping customers make informed and improved choices that work for them, offering a range of customisation options such as choosing our smallest size (Tall) and our oat dairy alternative with no added sugar.

Caffe Nero said its Belgian chocolate and hazelnut frappe creme is a "treat" adding that its iced latte, its highest seller, contained no added sugar.

A Costa Coffee spokeswoman said: “We are proud to offer a balanced range of drinks which also includes, as part of our summer menu, a fruity range of refreshers which all contain less than 40 calories and two teaspoons of added sugar per serving.

“We only offer our limited-edition seasonal drinks, including our summer range of frappes, in small and medium sizes.

“All drinks can also be customised to reduce the calorie or sugar content, including requesting skimmed milk and removing toppings, or downsizing to a smaller cup size