A spokesman for the AA accused Khan of misrepresenting the current regulations on out-of-home advertising in interviews he gave today around the announcement.
"While we welcome today’s announcement of the consultation, we do think it is important there is a fair representation of the facts around current regulation levels," the spokesman said.
"Unfortunately, this doesn’t appear to be the case, even with today’s announcement from the London Mayor’s office, where in interviews this morning, it has been suggested out of home advertising is not regulated in the same way as TV, for example."
Outsmart, the trade body for the out of home industry, pointed out that since last July, when new rules on HFSS came into force, it has prevented HFSS ads from appearing within 100 metres of a school - an exclusion that affects 14% of all static out-of-home sites in London.
ISBA also said it welcomed the opportunity to contribute to the consultation, but criticised Khan’s timing.
Phil Smith, director-general of the advertisers’ body, said: "The draft London Food Strategy preempts the Government's upcoming Childhood Obesity Strategy, expected in the coming weeks. We are proactively engaging with our members to ensure any policy outcomes are holistic, evidence-led and proportionate responses to reduce children’s exposure to HFSS products.
"This approach is already central to the self-regulatory system. Measures which intrude on an adult’s ability to make choices do not address the issue at hand or the current focus of government and regulators."
Khan’s advertising plan aims to tackle London’s high child overweight and obesity rates – with almost 40% of children aged 10 or 11 overweight or obese.
He was backed by figures including Jamie Oliver, former New York City mayor Michael Bloomberg, and Mumsnet founder Justine Roberts.
But the policy was blasted by transatlantic anti-regulation campaign group Consumer Choice Center, with managing director Fred Roeder calling it "heavy-handed and paternalistic".
He said: "Advertisement bans are a significant step towards censorship. Everyone wants to fight childhood obesity, but limiting the freedom of expression of the food industry and trampling on consumer choice isn't an appropriate solution."