UK-based anti-sugar campaign group Action on Sugar has claimed popular coffee chain Starbucks is serving hot drinks with dangerously high levels of sugar. The group conducted a survey on 131 hot flavoured drinks sold in UK retail outlets.

Starbucks was the top offender on Action on Sugar's list.

"The drink which was found to have the highest sugar content was Starbucks' Venti Grape with Chai, Orange and Cinnamon Hot Mulled Fruit, which had a total of 25 teaspoons of sugar per serving," the campaign group said.

Starbucks' Chai Latte Venti, which it promotes as a "healthy drink", had 13 teaspoons per serving, reported CNBC .

The survey has put the coffee company, which has 21, 000 stores in over 65 countries, in a tight spot.

A Starbucks spokeswoman told the Daily Mail: "Earlier this year we committed to reduce added sugar in our indulgent drinks by 25 percent by the end of 2020. We also offer a wide variety of lighter options, sugar-free syrups and sugar-free natural sweetener, and we display all nutritional information in-store and online."

Other eateries, including KFC and Costa Coffee, also figured on Action on Sugar's offenders' list.

The drinks assessed included flavoured coffees like mochas and lattes, hot fruit drinks and hot chocolates, which are widely bought from some of the UK's best-known coffee shops and fast-food chains, the Daily Mail report said.