The following sentencing guidelines refer to first time offenders, convicted after a trial and facing no other related charges. (Obviously that doesn't apply to you but the reference points which judges use start with those assumptions, before the judge moves the sentence up or down depending upon the specific circumstances).
The 'starting point' sentence for an offender convicted of a Section 18 offence, involving the use of a weapon
which came to hand at the scene is 5 years custody. Judges normally have to pass a sentence in the range of 4 to 6 years. If they don't, they must state their reasons in open court.
The 'starting point' where a weapon was
carried to the scene with specific intent to injure the victim is 8 years custody. Judges normally have to pass a sentence in the range of 7 to 10 years. (If that assault resulted in particularly grave or life threatening injuries, the 'starting point' rises to 13 years custody, with an anticipated sentencing range of 13 to 16 years).
Source:
http://www.sentencing-guidelines.gov.uk/docs/a ssault-against-the%20person.pdf
See the table on page 13
Chris