Some iced coffee drinks from high street chains can contain more sugar than a can of Coca-Cola, which contains 35g of sugar, a survey has found.

Which? compared frappes and frappucinos from Caffe Nero, Costa and Starbucks to find many had “exceptionally high” amounts of sugar.

A Starbucks caramel frappuccino with semi-skimmed milk was found to be one of the worst offenders, containing 48.5g of sugar – or 12 teaspoons’ worth.

NHS health advice suggests adults consume a maximum of 30g of sugar per day, or around seven teaspoons.

A Caffe Nero Belgian chocolate and hazelnut frappe creme contained 44.5g of sugar – equivalent to 11 teaspoons.

At Costa, a chocolate fudge brownie frappe mocha with oat milk included 42.6g of sugar, or 10.5 teaspoons.

Which? compared the amount of sugar in these drinks to a 51g Mars bar, which contains 31g of sugar (7.5 teaspoons), while a 330ml can of Coca-Cola contains 35g of sugar (around 8.5 teaspoons).

Even plain coffee flavour frappes and frappuccinos were found to contain “relatively high” amounts of sugar. A Costa Coffee frappe with skimmed milk contained 21.3g of sugar, Which? found.

While the calorie content of the drinks must be displayed in stores, the sugar content does not, which could leave consumers at risk of unwittingly exceeding the maximum recommended daily intake of free sugars, the watchdog said.

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

Health advice is to limit consumption of these sugars due to their potential to contribute to weight gain and tooth damage.

Which? suggested consumers wishing to cut their sugar intake switch to iced versions of a standard coffee instead.

The government introduced a Soft Drinks Industry Levy (SDIL) in 2018, known as the “sugar tax”, in an attempt to cut unhealthy levels of consumption.

However, some drinks are exempt from the tax, including fruit juices and drinks made on-site and served in open cups. Syrups, often used in frappes, are also exempt.

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, such as a standard iced coffee, which contains far less sugar.”

A Starbucks spokesperson 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.

“Sugar content for an Iced Latte with Semi Skimmed Milk, one of our most popular beverages, starts from 8.7g for a Tall size. Customers can find all nutritional information available on our mobile app, online and our menu boards.”

Caffe Nero described its Belgian chocolate and hazelnut frappe creme as a “treat” and said it accounted for less than 5 per cent of its sales of summer drinks, while “coffee over ice” drinks, which contained less than 8g of sugar, accounted for 50 per cent of summer drink sales.

The chain added that its iced latte – its highest seller – contained no added sugar.

Reporting by PA