Porridge and crumpets are among the products included in a pre-watershed ban of junk food ads under new legislation to tackle childhood obesity.

Details of the restrictions, unveiled on Tuesday, show that baked goods including crumpets, scones, croissants, pains au chocolat, pancakes and waffles are all considered junk food for the purposes of the laws.

Cakes including muffins, flapjacks and mini rolls will be banned, but icing and cake decorations are exempt, as is savoury bread and traditional loaves.

The restrictions also apply to sugary breakfast cereals including granola, muesli and “porridge oats, including instant porridge and other hot oat-based cereals”, while snacks including protein bars, cereal bars and biscuits will also be included in the ban.

Food and drink adverts will be banned if the products are classified as “less healthy” using a Government scoring system based on salt, fat, sugar and protein content.

In practice, it leaves room for healthy versions of products to continue to be advertised, such as porridge oats, but not those such as porridge products that have had sugar, salt or fat added to them.

Similarly, natural unsweetened yoghurt will not be subjected to the ban, but fruity and low-fat yoghurt or fromage frais will.

Listed alongside obviously unhealthy soft drinks including lemonades, colas and energy drinks are others that have added sugar including certain fruit juices and smoothies, milk-based drinks and milk substitute drinks such as soya, almond, oat, hemp, hazelnut or rice.

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

It will also apply to chickpea or lentil-based crisps, fried, flavoured or seasoned chickpeas, seaweed-based snacks and Bombay mix.

The ban comes into force from October next year, after which time television ads for junk food products will be allowed only after 9pm.

It will also include a ban on paid-for online ads for these products to reduce children’s exposure to foods high in fat, sugar or salt.

The Government has said it will prevent an estimated 20,000 cases of childhood obesity, and is expected to remove 7.2 billion calories a year from UK children’s diets.

Its impact assessment notes that “overall the studies do find a clear link between food advertising and calorie consumption”.

However, it also suggests that the measures could cut just 2.1 calories from children’s diets each day while costing advertisers £659 million in returns over 25 years.

It also warns that any calorie reductions achieved during childhood could be undone as individuals eat more during adulthood.

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.

“This is the first step to deliver a major shift in the focus of healthcare from sickness to prevention, and towards meeting our Government’s ambition to give every child a healthy, happy start to life.”

NHS data shows a trend of rising childhood obesity, with almost one in 10 reception-aged children (9.2%) now living with obesity and one in five by the age of five (23.7%) suffering tooth decay because of excess sugar consumption.

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.