London's East End youngsters are being intimidated by gangs - based on which postcode they live in.
Biko and Wez can get anxious crossing into E9
Teenagers marked as "E5" or "E9" risk being attacked for straying into the wrong area.
Simply crossing to the other side of a street which borders two postcodes could end in violence.
Teenagers Biko and Wez have to deal with the situation every day.
They are "E5" - and walking down the wrong road into neighbouring E9 could get them into trouble.
Wez told BBC London's Inside Out: "During the day it's alright, but when it gets late at night you start getting a bit anxious.
"I'm just worried about getting mugged... anything can happen out there."
Supt Logan says the attacks are a form of affiliation
Another teen - a girl who does not wish to be identified - has been the victim of two attacks.
"I was just walking down the road and I felt two people coming up behind me on a bike, she said.
"I turned round and one was a boy, one was a girl. They said to me: 'What Ends are you from?'.
"I said: 'I'm from north London but my dad lives two minutes away'.
"Just because I was two minutes away from where my dad lives across the border they took all my stuff, mugged me," she said.
Supt Leroy Logan, a police officer with more than a decade's experience on the beat in Hackney, said it was just a new way of creating boundaries.
Some teens are so intimidated they take long detours in order not to cross into "rival" postcodes, he said.
The problem is not confined to Hackney, say police
"If they know they have to go to another part of the borough and have to go through another postcode they'll take a bus looping round that area, or get people to drop them."
He puts it down to peer pressure and said police have been enlisting the help of teens to confront those trying to create the rivalries.
"It's not endemic in Hackney - it's in various boroughs across this country, and we've got various proactive initiatives, he added.
"We've got gang outreach workers really starting to find out what this beef is all about."