3. You've written "the police wouldnt take my statement . . . ".
If you believe that you can give evidence in court, to help your boyfriend's defence, you should contact his solicitor a.s.a.p.
4. You've written "My boyfriend is pleading self defence, since it was"
A court will normally won't accept 'self defence' as a justification for an assault unless it was clearly the absolute minimum course of action available to the defendant, which could ensure his own safety. It's also unlikely that such a plea would succeed if the defendant had initiated the sequence of events which led to the assault. (i.e. "my boyfriend tapped him across the back of his head").
5. If convicted, your boyfriend will be sentenced in accordance with this document. (A judge is only allowed to deviate from it under very exceptional circumstances):
http://sentencingcoun...person_accessible.pdf
See the tables on pages 13 (GBH with intent), 15 (GBH) and 17 (ABH). The sentences there refer to a first-time offender who is convicted after a trial. An early guilty plea can see sentences cut by one third but previous convictions can lead to higher sentences.
Chris