The magistrates' court can impose a prison sentence of up to 6 months. Or they can refer the case to the Crown Court, where the maximum penalty is 5 years imprisonment (plus a �5000 fine).
In practice, unless there are exceptional circumstances (e.g.a particularly sustained attack), a first offence of ABH hardly ever results in a custodial sentence.
Based upon reading loads of newspaper reports (and a bit of freelance court reporting myself) my guess would be something like a �200 fine + �60 costs + �15 victim surcharge + 200 hours unpaid work.
Chris