Chocolate manufacturers are planning to reduce the size of some of their best known brands by 20 per cent in a bid to comply with new guidelines on cutting sugar.

Companies such as Mars, Nestle and Cadbury plan to shrink the size of household name chocolate bars such as KitKats, Mars bars and Dairy Milk in order to reduce the level of sugar in them as part of a Public Health England plan to fight childhood obesity.

Although other producers of other high-sugar products such as yoghurt, fizzy drinks and breakfast cereal can change their recipes to add more artificial sweeteners chocolate manufacturers have warned this would ruin the taste of the bars – and could even have a laxative effect.

Following a meeting with PHE officials the big manufacturers have agreed to reduce the size of their bars to avoid being named and shamed in a report on childhood obesity which is due to be published next month, the Sunday Times reported.

The companies have reported not decided whether they will cut the prices of their products in line with the size reduction.

The targets set by the PHE will come on top of reductions already made by manufacturers and are due to be laid out in the report.

It said the percentage reduction will be calculated based on the average sugar content per 100g of product or reduction in product sizes.

The proposal to cut sugar was first introduced in July 2016 but was branded “pathetic” by some obesity campaigners who said the sugar content in food should be halved and fat content should be reduced by 20 per cent.

The amounts of sugar in food and drink Show all 6 1 /6 The amounts of sugar in food and drink The amounts of sugar in food and drink Minstrels A 42g bag contains 28.9g of sugar The amounts of sugar in food and drink Dairy Milk A 49g bar contains 26.8g of sugar The amounts of sugar in food and drink Skittles 45g of Skittles (about a quarter of a large 174g pouch) contains 40.4g of sugar The amounts of sugar in food and drink Ribena A 500ml bottle of Blackcurrant Ribena contains 23g of sugar, down from 50g/500ml after it was reformulated to avoid the government's tax on sugary drinks The amounts of sugar in food and drink Coca Cola A 330ml can of Coca Cola contains 35g of sugar The amounts of sugar in food and drink Innocent Smoothies A 250ml bottle of strawberries & bananas Innocent Smoothie (the middle size) contains 26g of sugar

Action on Sugar said the Government had also failing to set out plans to control food advertising: “[It] merely says there will be a consultation, which is a pathetic response, given the billions of pounds the food industry spends on advertising to young children of unhealthy products.”

The chairman of the group Professor Graham MacGregor, an expert in cardiovascular medicine at Queen Mary University said: “There's no justification for advertising unhealthy food to children, they're a very vulnerable group.”