Junk food adverts are banned on television and online starting on Monday as part of a drive to tackle childhood obesity.

The UK-wide ban stops food and drinks high in fat, salt and sugar (HFSS) being advertised on TV before 21:00 and at any time online.

It applies to products considered to be the biggest drivers of childhood obesity, including soft drinks, chocolates and sweets, pizzas and ice creams.

The Food and Drink Federation (FDF) said it is committed to helping people eat healthily and has been voluntarily abiding by the new restrictions since October.

As well as more obviously unhealthy foods, the ban also covers some breakfast cereals and porridges, sweetened bread products, and main meals and sandwiches.

Decisions over which products fall under the ban are based on a scoring tool, balancing their nutrient levels against whether they are high in saturated fat, salt, or sugar.

Plain oats and most porridge, muesli and granola are not banned under the crackdown, but some versions with added sugar, chocolate or syrup could be affected.

Firms can still promote healthier versions of banned products, which the government hopes will lead to food makers developing healthier recipes.

The ban only covers adverts in which unhealthy products can be seen by viewers, meaning fast-food firms will still be able to advertise using their brand name.

Previously, HFSS food and drink adverts were banned on any platform where more than a quarter of the audience was under 16.

Firms that do not comply with the new rules risk action by the Advertising Standards Authority (ASA).

NHS data shows almost one in 10 (9.2%) reception-aged children are now living with obesity, while one in five children have tooth decay by the age of five.

It is estimated obesity costs the NHS more than £11bn every year.

Evidence shows children’s exposure to ads for unhealthy food can influence what they eat from a young age, in turn putting them at greater risk of becoming overweight or obese.

The government estimates the ad ban will prevent around 20,000 cases of childhood obesity.

Katherine Brown, professor of behaviour change in health at the University of Hertfordshire, said the ban was “long overdue and a move in the right direction”.

She said: “Children are highly susceptible to aggressive marketing of unhealthy foods and exposure to them puts them at greater risk of developing obesity and associated chronic diseases.”

Ms Brown called for the government to make nutritious options “more affordable, accessible and appealing”.

The FDF said manufacturers are “committed to working in partnership with the government and others to help people make healthier choices”.

It added: “Investing in developing healthier products has been a key priority for food and drink manufacturers for many years and as a result, our members’ products now have a third of the salt and sugar and a quarter of the calories than they did ten years ago.”

Get our flagship newsletter with all the headlines you need to start the day. Sign up here.