This type of behaviour is becoming quite common on public transport. I'm sure the driver is just hoping to get through his working day without being stabbed and is, naturally, unwilling to assert him/herself.
The failure of the driver to help create a (perceived) safe environment on the bus means that paasengers, especially, the vulnerable ones like lone women, old, disabled and the very young are seriously intimidated . . . or assaulted (or worse).
CCTV by itself is NOT EFFECTIVE in combatting anti-social behaviour on public transport unless it is instantly stopped and prosecuted.
There is no point in fuming, we need to encourage our local political leaders to start getting tough. Some routes can do with special conductors accompanying drivers, especially, at night when the various clubs/bars spew their drunken hordes out on to the streets for the police and transport infrastructure to deal with. Ofcourse, we're all paying for it . . .