Would you like a proper answer to your question?
The guideline 'starting point' when sentencing a 'Section 18' offence, with the circumstances you've described, is 5 years custody, with judges normally expected to pass a sentence in the range of 4 to 6 years. The element of 'provocation' might make the judge want to consider a sentence at the lower end of the range.
However, those sentences refer to first-time offenders who've been convicted after a trial. An early guilty plea would result in a reduction of the sentence but a previous convictions for violence could see it increased.
Based on that lot (and assuming an early gulty plea with a reasonably clean previous record), my guess would be a sentence of
between 3� and 5 years imprisonment.
Source:
http://www.sentencing-guidelines.gov.uk/docs/a ssault-against-the%20person.pdf
(See the table on page 13)
Chris