Details of the restrictions show baked goods including crumpets, scones and pancakes are all considered junk food under the new legislation.
Adverts for sugary breakfast cereals will also disappear from pre-watershed television screens, with granola, muesli and "porridge oats, including instant porridge and other hot oat-based cereals" all classed as "less healthy" food.
The promotion of sweetened yoghurts and sugary drinks – including fizzy drinks and some fruit juices – will also be restricted.
The government will classify products according to a scoring system based on their sugar, fat and protein content, banning advertising on all foods designated as "less healthy".
This means healthy versions of products – including porridge products with no added sugar, salt or fat, and unsweetened yoghurt products – will not be subject to the ban.
As well as TV advertising, the new legislation applies to paid-for online ads for these products to reduce children's exposure to foods high in fat, sugar or salt.
The legislation comes in the context of rising childhood obesity levels in the UK, with NHS data suggesting almost one in 10 reception-aged children (9.2%) lives with obesity.
One in five children by the age of five (23.7%) suffers tooth decay because of excess sugar consumption, NHS figures indicate.
Former prime minister Boris Johnson first announced a UK-wide ban on TV adverts for food high in sugar, salt and fat before 21:00 to help tackle the problem in 2021.
The ban was later delayed to 2025, with the Conservative government saying it wanted to give the food and drink industry time to prepare for the change because of the cost of living crisis.
