You can find the guidelines here
http://sentencingcoun...ine_-_Crown_Court.pdf
It depends on whether "serious injury" has been caused and whether higher or lower culpability is present.
Factors like a single blow might indicate lower culpability for example but you'll see from the document.
Those 2 factors give you either a category 1,2 or 3 offence
The *starting* point and variations for each is:
Category 1 - 12 years’ custody can be 9–16 years’ custody
Category 2 - 6 years’ custody can be 5–9 years’ custody
Category 3 - 4 years’ custody can be 3–5 years’ custody