Louis Tomlinson 22, films the footage as he announces: 'So here we are, leaving Peru. Joint lit. Happy days!'
Meanwhile his bandmate Zayn Malik, 21, responds: 'very controversial' as he is seen smoking the roll up in the back of the band's SUV.
The footage is likely to shock the stars' millions of young fans - whose parents will also no doubt be questioning the group's previously squeaky clean image.
Questions are also being raised about whether the two band members featured in the video will be able to enter the U.S. this summer, where they are due to tour.
'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.'
As the pair travel in the SUV, a member of the team who is with them asks: 'Are we allowed to talk contraband in this?' before Louis replies: 'Yes, that's what it is about.'
Tomlinson even credits the joint as being an important part of Zayn's pre-show warm up.
The pair are seen joking as they watch police motorcyclists pass them outside the car, with Louis giggling: '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.'
Picture from MailOnline exclusive video.