Other than in genuinely exceptional circumstances (which the judge must explain in open court) a judge must use the starting point referred to below and then move the sentence up or down between the minimum and maximum points shown. However it should be noted that the sentences refer to a first time offender, convicted after a trial. Previous convictions (especially for violence)can push the sentencing range higher but an early guilty plea cab see one third cut from the sentence. (Remember, as well, that the time spent in prison is usually one half of the actual sentence term).
For the lowest level of 'Section 18' offences, the starting point is 4 years imprisonment , with a minimum of 3 years and a maximum of 5 year.
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.
There is a higher category but it would seem not to be relevant to your case.
To see the difference between 'Section 20' (GBH) and 'Section 18' (GBH with intent), read paragraphs 50 to 67 of this document:
http://www.cps.gov.uk...on/#Unlawful_wounding
Chris