Unlike some others around here, I'll try to answer your actual question regarding what you could be facing.
The first thing to consider is the nature of any possible charge. Although you seem to have been bailed 'on suspicion of causing actual bodily harm', that doesn't mean that 'ABH' would automatically be what you could be charged with. A fractured skull normal comes into the category of 'GBH'.
To see the type of injuries which constitute ABH, read paragraph 46 here:
http://www.cps.gov.uk/legal/l_to_o/offences_ag ainst_the_person/#P189_14382
Then scroll down to paragraph 55 to see the type of injuries which constitute GBH. (Note the specific reference to a fractured skull).
Courts are normally constrained in their sentencing by official guidelines. They are given a 'starting point' sentence, based upon a first-time offender being found guilty after a trial. (A lesser sentence will be passed upon someone pleading guilty at an early stage. In the case of custodial sentences that means up to one third off the sentence). They are also given a 'range' of sentences, which the court can't go outside unless the magistrates or judge provide an explanation for their decision in open court.
To see the 'starting points' and 'ranges' for different categories of ABH offences, see page 17 of this document:
http://www.sentencing-guidelines.gov.uk/docs/a ssault-against-the%20person.pdf
If the charge is 'GBH' (under 'Section 20') refer, instead, to page 15 of that document. If the charge is 'GBH with intent' (under 'Section 18'), refer to page 13.
Chris