A new ban on junk food advertising on TV and online will cut just two calories a day from children’s diets – equal to less than a tenth of a jelly baby.

Ministers will today introduce legislation curbing the commercials despite acknowledging it could cost firms £199 million a year while having a marginal impact on diets.

The policy is aimed at reducing children’s exposure to foods that are high in fat, sugar or salt, such as cakes, biscuits, ready meals and crisps.

It will come into effect from October next year and apply to advertising on TV before the 9pm watershed and on the internet at all times.

The Government’s impact assessment says the measures are likely to reduce children’s exposure to such adverts by just 8.9 seconds and cut 2.1 calories from their diet each day.

Taken as a whole, the Department of Health and Social Care says this could prevent 20,000 cases of childhood obesity. However, its impact assessment notes the true benefits may be less, saying youngsters may make up the calorie deficit by eating more as adults and advertisers could lose £659 million over 25 years.

Officials will today also publish a detailed list of the food and drinks that will be subject to the ban.

It includes prepared soft drinks containing added sugar; savoury snacks; breakfast cereals and porridges; chocolates and sweets; ice cream, ice lollies, frozen yoghurt, and cakes. 

Adverts for sweet biscuits and bars based on nuts, seeds or cereal will also be restricted, as will morning goods including sweet pastries and sweetened bread products; desserts and puddings; sweetened yoghurt and fromage frais; pizzas; prepared potato products; and ready meals and sandwiches.

Health Secretary Wes Streeting said: ‘Obesity robs our kids of the best possible start in life, sets them up for a lifetime of health problems, and costs the NHS billions. This Government is taking action now to end the targeting of junk food ads at kids, across both TV and online.’

NHS data shows a trend of rising childhood obesity, with almost one in ten reception-aged children (9.2 per cent) now living with obesity and one in five by the age of five (23.7 per cent) suffering tooth decay. 

Professor Sir Stephen Powis, NHS national medical director, said: ‘We’ve always said the NHS can play its part in supporting people who are obese to reach a healthier weight, but we need to work with the rest of society to prevent people becoming overweight in the first place. So we welcome this proposed legislation and look forward to working with the Government and partners to help protect the good health of future generations.’

Children with obesity are said to be more likely to live with the condition as adults and to be at significantly greater risk of life-limiting illnesses.

Obesity is the second biggest preventable cause of cancer, according to health experts, costs the UK health service more than £11 billion each year, and is a major contributor to ill health that prevents people from participating fully in work.

Chris Snowdon, head of lifestyle economics at the Institute of Economic Affairs, said: ‘The ban on food advertising has no global precedent so Britain is in uncharted territory, but I predict that it will not lead to a reduction in obesity. Every other anti-obesity policy has failed, including the sugar tax and mandatory calorie labelling, and I see no reason why this will be any different.

‘It is bad news for broadcasters, internet platforms and for everyone who uses them. If, in five years’ time, obesity rates have not fallen, the ban should be repealed and serious questions should be asked of the pressure groups who pushed for it.’

A spokesman for the Advertising Association said: ‘The Government’s own impact assessment makes clear this policy’s impact on daily calorie reduction for the average child will be minimal at best while potentially costing the UK advertising sector millions of pounds, impacting on the UK’s creative industries and wider economic growth.

‘We urge the Government to implement holistic policies proven to address true causes of obesity such as socio-economic deprivation and public health campaigns can play an important role.’