Sorry I forgot to add that ABH is a compound offence! It is comprised of a battery or assault with the effect of there being actual bodily harm caused (or in the cause of assault there will be some emotional distress caused - there’s caselaw on what level of harm there needs to be here but to be honest I forget the precise details).
This has a huge effect on the level of intention - the intention for battery or assault is the intention for ABH, so it can be distinguished from GBH in that often the person inflicting ABH won’t intend to do so, whereas with GBH they have to intend to cause some harm, albeit not serious harm (s20) or cause serious harm (s18).