The following sentences refer to an adult first time offender convicted after a trial. Previous offences (particularly for violence) can push the sentencing higher. An early guilty plea can see a sentence cut by one third:
The 'starting point' sentence for the most basic of GBH offences (i.e. where no weapon was used, where there was no pre-meditation and where the victim's injuries were not 'particularly grave') is 24 weeks imprisonment, with judges expected to pass an actual sentence ranging from a 'high level' community order up to 36 weeks imprisonment.
Where the victim's injuries are regarded by the court as 'particularly grave' (but the other circumstances are unchanged) the 'starting point' is 18 months, with judges expected to pass a sentence between 12 months and 3 years.
The actual time spent in prison is normally half of the nominal sentence.
Chris