Not quite, Ethel. S 18 is wounding or causing grievous bodily harm with intent to do some grievous bodily harm (or with intent to resist the lawful detainer or apprehension of somebody). It's not with intent to kill. If it were, the offence would be attempted murder.( What is confusing is that someone who commits what would be the s18 offence, not intending to kill, but , in fact , by doing so causes the death of the victim, is guilty of murder.)
Nothing is certain but a bad s20 attracts a custodial sentence.It's impossible to say in this case because so much depends on the circumstances of the offence and the offender.