Researchers develop guidance to tackle ‘high carbon’ advertising on London’s transport network

Researchers have answered the Mayor of London’s call for guidance regarding a possible ban on the advertising of ‘high carbon’ products and services on the capital’s public transport network.

A team of academics led by UWE Bristol’s Tom Youngman have produced recommendations to assist with a decision on a potential ban on contentious billboard advertisements on the Tube, overground railway and bus network to meet climate goals.

Examples of high carbon advertising include messages promoting flights, deforestation-linked foods and petrol cars. Many of these adverts are viewed as to detrimental to efforts for London to reach net zero greenhouse gas emissions by 2030.

Researchers say Transport for London (TfL) has the legal power to implement a ban on high carbon advertising, as does the Mayor of London Sadiq Khan to direct it to do so. But he has previously stated that introducing any ban would be difficult as there is a ‘lack of clarity’ on what constitutes high carbon advertising and has called for the drafting of national guidance.

To address the absence of a definition, Tom Youngman worked with UWE Bristol colleagues Katie Allen, Laura McAllister, Stelina Kanaki and Tim Gale, to come up with robust suggestions that the Mayor of London could consider.

They considered a longlist of 36 possible definitions, applying systematic screening to whittle down the longlist to a shortlist of five. Reflecting on their shortlisted definitions, they proposed a combination of these definitions as most likely to be effective in contributing to London’s 2030 net zero goal:

High Carbon advertising shall be defined as any advertisement meeting one or more of the following criteria:

1. Adverts from advertisers operating primarily within a high carbon sector.
2. Adverts for, or depicting, high carbon products or services.
3. Adverts which could be reasonably interpreted as encouraging high carbon behaviours.

In their report on their work, funded by Adfree Cities, the academics say that the TfL’s Advertising Steering Group should be given a mandate to make the final call on whether to decline contentious advertisements.

TfL has already implemented a range of advertising restrictions. For example, Sadiq Khan made a ban on adverts that promote negative or unhealthy body image an election campaign promise, which he followed through with in 2017, and introduced a ban on advertising high fat, salt and sugar (HFSS) foods in 2019. HFSS foods is the most common reason TfL gives for declining advertising campaigns - being cited for 21 of the 51 refusals in 2024/25.

But several UK cities are ahead of London when it comes to introducing bans on high carbon, or fossil fuel, advertising. In 2024, Edinburgh banned advertising for fossil fuel companies, airlines, airports, fossil fuel-powered cars, SUVs and cruise ships on council-owned advertising spaces, while Sheffield and Portsmouth have also introduced bans.

Tom Youngman, an environmental economist and a research fellow in UWE Bristol’s School of Applied Sciences, said he hoped that the evidence-based recommendations that he and the UWE Bristol team have produced would set a gold standard for a high carbon advertising ban definition in the UK.

He explained: “The fact that there's not a more research-led systematic definition means that councils are currently having to be less ambitious. They're doing what they think they can justify and they've not got any wider kind of evidence to back it up.

“We're hoping that our report, which scopes out the full space, gives a clearer sense of why councils should go for a definition more akin to what Edinburgh and Sheffield have introduced. We hope that some councils with weaker definitions might improve their definitions on the statute book, as well as giving other authorities such as Transport for London the confidence to implement the definition of a restriction for the first time.”

The report by the UWE Bristol academics highlighted that only 0.3 per cent of total advertisements are currently rejected by TfL.

Tom said: “The high carbon advertising on Transport for London is prominent, but it's not dominant. It's not like every advert is for a huge petrol car or for luxury flights. They have a mix and it ranges from advertising for West End shows and musicals to clothes, fashion and all sorts. The fact that they are diversified in their clients means they have the headroom to make this choice. They can afford to be more discerning.”

But the academic admitted it had been a highly challenging exercise to land on a workable definition and stressed there would be difficulties in introducing any ban.

Tom added: “Business is often done in a way that most effectively juggles the legal requirements placed upon companies – and rules about advertising will be no exception. There will be real implementation challenges.

“The way that bans have been addressed by TfL on other issues has usually been to use discretion. That's why our recommendation opted to go for a three-pronged multifaceted definition that provides three ways of capturing the issue. If you've got three sets of criteria, it means you don't have to have one razor sharp rule.

“This area still requires further research. Our piece of work was aimed at trying to come up with ideas for scoping out the space and putting forward a definition that’s more rigorous than what's been put forward so far. The real test will be putting something into practise and seeing how it performs.”