I rather expect a lot will depend on what his past history is.
I'd be surprised from what you say if he's an otherwise upstanding member of the community with a good job and just got drunk one night!
Most likely already got a history of violence and might even be out on parole.
From this post of Chris' a few years back he notes that kicking counts as using a weapon that came to hand
http://www.theanswerbank.co.uk/Law/Question930989.html
// Where the victim suffered a very serious injury or permanent disfigurement OR there was pre-meditated wounding or GBH OR other wounding or GBH involving the use of a weapon that came to hand at the scene:
SP = 5 years
Min = 4 year
Max = 6 years
(It should be noted that kicking someone, while wearing shoes or boots, may be regarded as 'using a weapon which came to hand at the scene').
If the victim suffered life-threatening injury or particularly grave injury:
SP = 8 years
Min = 7 years
Max= 10 years //
So if things are more or less the same it'll also depend on whether the injury was considered life threatening or particularly grave
I wouldn't like to speculate on that but it looks as if disfigurement alone is enough to qualify for that - I'd guess it's more likely to be the former but who knows.
Based on that maybe 5-6 years?