Junk food advertising could be banned across the Transport for London network, in plans praised by celebrity chef Jamie Oliver as a "game-changing moment".
The Mayor of London announced the proposal today as a bid to tackle the "ticking timebomb" of childhood obesity.
The capital has one of the highest childhood obesity rates in Europe, with almost 40% of children aged 10 or 11 overweight or obese.
If approved the proposals could see adverts for food and drink high in fat, salt or sugar banned across the London Underground, London Overground, buses and bus shelters.
Oliver launched his #adenough campaign last month calling for the introduction of a 9pm watershed on junk food advertising on television and controls over where adverts can be placed in public areas and on transport.
Responding to the announcement he said: "Sadiq Khan today takes a massive and bold step forward for child health in London. This is a game-changing moment, protecting kids from relentless junk food advertising on their daily journeys to school and around our amazing city. Putting their health first shows others what strong leadership looks like.
"London now has the most overweight and obese children of any major global city. Sadiq is starting to use everything within his power to tackle this head on. This surely must give Mrs May and her cabinet inspiration to do the right thing, be bold, be clear, and pull every lever they can to protect all British kids. Now is the time!"
Calling on the government to act against childhood obesity Khan added: "Child obesity in London is a ticking timebomb and I am determined to act. If we don't take bold steps against it we are not doing right by our young people as well as placing a huge strain on our already pressurised health service in years to come.
"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."
A McDonald's spokesperson responded to the proposal saying: "We share the Mayor's ambition to reduce childhood obesity in the capital and are committed to helping our customers to make informed choices. Obesity is a complex issue and is one that has many contributing factors.