in fact, hmp isis is said to have more than 130 gangs. slashed and his throat slashed. by hmp isis in london, in his car, we speak to a man who's been visiting a relative. he tells us the relative is the victim of a vicious gang fight. we've had to revoice his words because of the threat posed to his family member. he hasn't been out of his cell for two days because there's been eight stabbings on the wings over the gang fighting. postcode gangs, drug gangs, religious gangs — they're often put on different wings, but some prison officers say a shortage of cells means this isn't always possible. they say it's leading to more violence as rival groups are sharing the same area. on our recent visit to hmp pentonville in london... 0h! the smell of the drugs in here. ..confiscated cannabis and weapons used by gangs. tell me what you've got here. 0k. what we've got is weapons that have been fashioned by prisoners whilst they're in the custody. we've got the toilet brushes here where they've had razor blades melted into them. this could do some r