arrested for assaulting a doorman, how to prove self defence and innocence

[DivvyP]

in a nightclub 19.05.07,my boyfriend got thrown out (he was trying to take a flashing badge off his shirt,didn't manage it so took off his shirt to remove it,doorman kicked him out for not wearing shirt)he walked away from nightclub entrance about 20-30 steps away (waiting for me to come out of the club.saw him getting thrown out), within a few seconds a doorman came towards him, fists clenched, shouting at him.My boyfriend started to walk backwards to move away from the doorman but still facing him, the doorman went to hit my boyfriend as the doorman was about to throw a punch,my boyfriends instant reactions was to put his fists up and swing back. He didn't mean to hit him in the face.My boyfriend did NOT continue hitting him,was shocked that he had hit doorman,(who was on the floor),boyfriend got jumped by other doormen, was punched many times & bitten on his back.police arrived & boyfriend&was arrested for assault.
Injured doorman has got a fractured cheekbone & will need an operation. My boyfriend has not been charged, has been released on unconditioned bail cuz police need to collect evidence.
What happens if :
A) There is no evidence (CCTV) showing the hit & showing my boyfriend moving backwards.
B) If the statements available are from the other doormen only & there are no independant witnesses
C) What if the injured doorman gets a false independent witness?
D) How long do the police have before deciding on whether to charge him or not?
Have gone back to police & asked officer to request CCTV footage from another pub camera (hoping something will have been picked up)the club CCTV hasn't been given,has been requested by the police (twice). It seems we are constantly trying to prove his innocence. What happen to innocent until proven guilty?
Any advice on this matter will be appreciated it. I'm extremely worried about it.