The UK’s top graffiti cop, Detective Constable Colin Saysell, is advocating for harsher penalties to be levied against graffiti writers and street artists who chose to make their works in unauthorized spaces.

Speaking at a conference on graffiti at London’s Southbank center, he said that the authorities should impose lengthy prison sentences on individuals arrested for graffitiing buildings and cited a recent case in which five such individuals were sentenced to a combined 11 years behind bars.

“Those kind of sentences have a deterrent effect … Some writers just quit. Others radically changed the way they operated—they decided to go abroad to other countries that have different attitudes to graffiti,” he said, according to a report in the Guardian.

The paper claims Saysell has arrested more than 300 graffiti writers in his career, which has also seen him travel to Europe to advise other police forces on methods to combat vandalism. He claims that graffiti is a gateway drug of sorts to a life of crime, explaining that “it leads to other forms of urban decay and it creates a climate of fear.”

Street artists producing work for galleries and not on building-sides needn’t fear Saysell’s wrath, however. Though he still doesn’t sound particularly keen on the genre, Saysell says that if prominent graffiti artists want “to produce lovely canvases and give them to leaders of countries like the US, it’s nothing to do with me. Graffiti is only ever graffiti when it’s done illegally.”