Unless there are very unusual circumstances (which the judge must explain to the public in open court) the judge MUST stick to the guidelines for Section 18 sentencing on page 5 of this document:
http://sentencingcoun...ine_-_Crown_Court.pdf
(See page for a definition of the the categories).
The sentences there refer to a first-time offender who is convicted after a trial. (Previous convictions can push sentencing higher. An early guilty plea can see the sentence cut by one third).
Given the nature of the injuries I reckon that you've got no chance whatsoever of getting the charge/conviction down to Section 47 and, given the sustained attack, you've also got no chance of Section 20 either. See this document for the definitions used by the CPS. (They're not actual law but they're based upon the decisions of the courts in countless cases):
http://www.cps.gov.uk...s_against_the_person/
My guess is that the sustained assault (but with no permanent harm) will make it a 'Category 2' offence, for which you're probably facing a sentence of 5 to 6 years imprisonment. (If so, you could be considered for release from prison at the half-way point in the sentence but you might have to wait until the two-thirds point).
Chris