'GBH with intent' is akin to 'attempted murder' in that it carries a maximum sentence of life imprisonment so, unless the charge is dropped to 'ABH' or (less likely in the circumstances you describe) to 'GBH', you're in big trouble.
Start by reading up on the differences between 'ABH', 'GBH' and 'GBH with intent'. See paragraphs 45 to 67, here:
http://www.cps.gov.uk...s_against_the_person/
Then view the tables on pages 13, 15 and 17, here:
http://www.sentencing...inst-the%20person.pdf
The sentences shown in those tables refer to first-time offenders who are convicted after a trial. An early guilty plea can result in a one third reduction of the sentence. Judges are obliged to stick to those guidelines unless there are genuinely exceptional circumstances (which a judge must explain in open court).
Based upon those tables, if the charge remains as 'GBH with intent', the minimum sentence you would be likely to receive (assuming that you plead guilty) would be one of 2 years imprisonment, of which only 1 year would actually be spent 'inside'.
Chris