London Mayor Sadiq Khan has ordered the ban on advertising high fat, salt and sugar (HFSS) food and drinks because he wants to curb childhood obesity.

TfL has said it wants to help advertisers to navigate the new regulation and is "trying to be sympathetic" and to "make ourselves available" to answer questions.

The Advertising Association, which represents the UK ad industry, has warned some aspects of the HFSS policy are "complicated".

Here is Campaign’s guide to how it works: