The Metropolitan Police have issued new guidance to groups wishing to protest on the streets of London.
From the beginning of June, anyone wishing to march through the capital will be told not to smoke or face having their entire demonstration banned.
"We've found that those who smoke are the most violent of protestors." Chief Superintendent Steve Nalls told reporters. "We're particularly concerned for the safety of those who're planning marches which are expected to turn violent and where petrol bombs could be used. A lit cigarette is an obvious source of ignition and that is a potentially dangerous issue."
The guidance means that organisers of protests will have to guarantee that no-one will smoke from the start to the end of a planned demonstration; if smokers are identified lighting up during a march, they and the organisers will be arrested.
"This is a public safety issue and we're very keen to ensure that everyone has the ability to protest in a safe environment."
It's thought a march in July by the pro-smoking group FOREST will not be licensed.