The boy band pair joke about marijuana while smoking a suspicious looking self-rolled cigarette in a video made as they were reportedly being taken to Peru's Estadio Nacional in Lima on April 27.
In a video obtained by MailOnline.com, Louis says: ''So here we are, leaving Peru. Joint lit. Happy days!''
As the vehicle carrying the two band members makes it way through the streets, Louis , 22, spots a police motorcyclist, and says: ''That's the police. That's the po po. One-nil.''
As he coughs and smoke appears across the camera screen, he says: ''Smokescreen baby!''
As they pass another police officer, Louis says: ''One nil b***h! Look at this b***h! He's having a look. He's thinking, 'I'm sure I can smell an illegal substance in there.' And he's hit the nail on the head.''
Louis also passes the ''joint'' to Zayn, 21, announcing: ''Zayn takes his job very seriously. He makes sure he goes through a two hour intense warm-up before every show. Just to get himself in the zone for the show.
''One very very important factor of Zayn's warm up of course if Mary J. herself. In fact I will present it to him now for some fantastic singing.''
After he takes a drag on the roll-up, he says: ''nice.''
The clip could cause serious harm the band's squeaky-clean image, and will no doubt upset the parents of many of their younger fans.