The fast food giant says its new drink, called Fruitzz gives children one of their recommended five portions of fruit and veg a day.

But a 500ml cup contains 300 calories and 49 grams of sugar, while health bosses recommend that children have no more than 50 grams of sugar a day.

The drink is part of the chain’s efforts to improve its health credentials when it comes to children’s meals and follows the addition of carrot sticks, fruit bags, mineral water and organic semi-skimmed milk to its Happy Meal menu.

Dietitian Christina Merryfield, from Bupa Cromwell Hospital, London, said: “’A large cup of this drink has more sugar than a can of Fanta.

“Sugary drinks can encourage tooth decay and erosion and lead to weight gain. Water is a much better option and milk is great because it is full of calcium and other vitamins and minerals.”

Tam Fry from the National Obesity Forum said: “For a drink purporting to be healthy having this much sugar is appalling. The danger to children is incredible.”

The fast food chain’s chief executive and president Jill McDonald said: “For the past three years, we have been working hard behind the scenes to create a fizzy drink that is unlike anything else currently available in high street restaurants.

“We tried and tested 80 formulations in order to create the right product that delivers nutritional benefit as well as a new, exciting taste.”

A McDonald’s spokesman added: “It is very difficult to reduce the calorie content of fruit juice without introducing artificial sweeteners.”