The recommended sentence for Actual Bodily Harm is a custodial sentence:
Mittigating factors include: Minor injury (I guess that's not the case here as GBH is being considerred), Provocation, A single blow ( 4 counts - not you again).
Aggravating factors include: Abuse of trust (domestic setting),Deliberate kicking or biting,Extensive injuries (may be psychological), Headbutting,Group action,Offender in position of authority, On hospital/medical or school premises, Premeditated,Victim particularly vulnerable, Victim serving the public,Weapon
Don't know if any of these apply.
Mitigating factors include: Age, health (physical or mental)
Co-operation with police, Evidence of genuine remorse
Voluntary compensation.
The maximum sentence a magistrate can give is 6 months but they can send you for sentence of up to 5 years.
GBH under section 18 involves intent - that is they must show you intended to cause serious bodily harm and can attract a life sentence - but I doubt that's what you're being considerred for. Under section 20 they only have to show you acted recklessly - maximum sentence 5 years.
The following are the min, max and average terms in months for the year 2003
.........................Min.............Average..............Max
ABH..................0.5............... 9.2.....................60
GBH(intent).......6..................50....................life
GBH................ 0.9..................18...................60
Hopefully you can make a guess yourself from that knowing the circumstances