These are the sentensing guidelines:
http://www.sentencing-guidelines.gov.uk/docs/V ersion%20for%20publication%202007-02-16.LD.pdf
4. In addition to showing that the offence resulted in grievous bodily harm, the prosecution must prove that the offender had a specific intent to cause that level of harm. The CPS suggests that factors which may indicate a specific intent include:
a repeated or planned attack;
deliberate selection of a weapon or adaptation of an article to cause
such as breaking a glass before an attack;
making prior threats;
using an offensive weapon against, or kicking, the victim's head.
Doesn't sound all that relevant but I'm not an expert.
The summary