If the offence was simply 'GBH' (rather than 'GBH with intent', which carries higher sentences), the 'starting point' sentence for a 'Category 3' (lowest level) GBH offence is 'High Level' Community Order (= 'probation'). Within that category, the judge can actually pass a sentence between a 'Low Level' Community Order and 51 weeks imprisonment.
See the table on page 8 of this document for sentences for higher categories of GBH. (See page 5 for the table relating to GBH with intent):
http://sentencingcoun...ine_-_Crown_Court.pdf
'Ordinary' GBH is an 'either way' offence, which means that it can be dealt with either in a Magistrates Court or before the Crown Court. (GBH with intent has to be dealt with in the Crown Court). The fact that the case has been referred to the Crown Court indicates that the Magistrates have decided that their sentencing powers (of up to 6 months imprisonment) might not be great enough. However that should not be construed as meaning that a lengthy prison sentence is inevitable. (The Crown Court often passes a non-custodial sentence after the Magistrates have passed a case up to the higher level).
Chris