If I was you I would plead not guilty in the sense you were provoked! To many statements are needed in your case because alot of people were involved, all drunk and in the early hours of the morning. There will be to many discrepancies in their statements and your solicitor will play on these. Don't be afraid to plead not guilty, they have to prove you guilty beyond resonable doubt, how can they prove you weren't provoked or felt in danger yourself!
I am going through the same thing myself at the minute only a bit more serious. I am pleading not guilty. A guilty plea might get you "UP TO" a third off (maybe nothing), a not guilty plea might get you off.
If they courts thing you might or could of been provoked or felt in danger they will have to left you off because there is reasonable doubt! The CPS might argue you used excess force though but you can argue you felt in danger for your life as they were getting up and acting aggressive, swearing etc. They might not even turn up to court and it gets thrown out, but if you plead guilty they don't need to turn up.