Some of the UK’s biggest food companies have attacked a plan that could see all online junk food advertising banned to tackle childhood obesity.

In a letter to the prime minister, bosses of firms including Britvic, Kellogg’s and Mars said they supported government efforts to tackle obesity.

But they said the plans were “disproportionate” and lacked evidence.

The government has said it is determined to help children and families make “healthier choices”.

It originally planned to ban online adverts and TV commercials for unhealthy foods that appeared before 9pm, but strengthened this in November.

The prime minister is said to have changed course after being hospitalised with Covid-19, something he links to being overweight.

The proposal, which is still under consultation, could usher in some of the toughest digital marketing restrictions in the world by the end of 2022.

Advertising for foods high in fat, salt or sugar would be banned from platforms such as Facebook, in paid search results on Google, in text promotions and in posts on platforms such as Twitter and Instagram.