Mayor of London Sadiq Khan has unveiled plans to ban junk food adverts on the capital’s trains and buses in a bid to crack down on “the ticking timebomb” of child obesity in the city.

The proposals, which would be the largest intervention of its type in any city in the world, would prohibit adverts for foods and drink classed as “unhealthy” by the Food Standards Agency – namely foods such as chocolate, crisps and most fizzy drinks.

Such a ban would exclude alcohol advertisements.

The Mayor of London said: “It can’t be right that in a city as prosperous as London that where you live and the income you have can have a massive impact on whether you have access to healthy, nutritious food and your exposure to junk food advertising.

“I’m determined to do all I can to tackle this issue with the powers I have and help Londoners make healthy food choices for themselves and their families.”

He added that he wanted to “reduce the influence” on children and their families by banning advertisements for unhealthy food and drink that are high in fat, salt or sugar across the entire Transport for London network.

His plans, part of his draft London Food Strategy which aims to reduce the level of child obesity in the capital by 2028, will now be subject to a consultation.

He is also proposing a ban on new hot food takeaways opening within 400 metres of schools.

Such a move was introduced by Redbridge Council health bosses in January last year and has been heralded as a major success.

Professor Dame Sally Davies, the Chief Medical Officer for England, said: “The evidence is clear that although it is not a silver bullet, restricting the amount of junk food adverts children are exposed to will help reduce obesity.

“Children are inundated with adverts for unhealthy food so this is a really encouraging move and a bold step in the right direction.”

Justine Roberts, founder of Mumsnet, said parents would be grateful for measures that reduce “pester power”.

She added: “Food manufacturers have done well in bringing down salt levels in everyday foods, making it easier for families to be healthier; it would be great if they could collectively act on sugar and fat to help parents ensure that children have a balanced diet.”

London has one of the highest child overweight and obesity rates in Europe, with 38.6pc of children aged 10 and 11 across the capital overweight or obese.

East London boroughs in particular have struggled to take on the problem.

Shockingly, 44.3pc of Year 6 pupils in Barking and Dagenham are classed as overweight or obese – the joint worst record in London.

Young children in Tower Hamlets aren’t far behind, with 42.2pc of 10 and 11-year-olds coming in at unhealthy weights.

Despite recent successes banning chicken shops near schools, Redbridge still came in over the London average for child obesity, with 39.2pc of youngsters either obese or overweight.

And although it performed better than all its neighbouring boroughs, Havering was still slightly above the city-wide average for obesity in children, recording 39.2pc.

Havering Council bases its own Prevention of Obesity Strategy around three key areas: Shaping the environment to promote healthy eating, supporting a culture that sees physical activity and healthy eating as the norm, and prompting individuals to change, primarily through self-help.

The council also established a permanent subgroup of the Health and Wellbeing Board two years ago to focus solely on tackling obesity.

In the foreword to the council’s strategy document, Councillor Wendy Brice-Thompson insisted everyone involved was working hard to “bring the obesity epidemic under control”.

She said: “Austerity isn’t a reason for doing nothing - it makes the case for action all the more persuasive.

“The solution isn’t investment in new specialist services.

“Rather everyone must do their bit, every day, in terms of the decisions they make, the advice they give and the actions they take to promote healthy eating and greater physical activity.”