Here you go, have a read, its aimed at youths, but it'll give you an idea of the processes involved:
http://www.walsall.gov.uk/index/if_you_get_arrested.htm
For something serious like assault, you get charged by the police and then sent to court. You wont get a court date the next day, it takes months for the CPS to get their act together.
Also when you have to appear in court you have to be given a written letter stating the date and time. They have to leave sufficient time between you receiving this letter and your court appearance so that you can arrange days off work, a childminder, whatever.
Now don't get me wrong, I wish the justice system in this country could turn criminals around in 2 days, like in your OP, but that's simply not the case. It takes months and is a long tiresome process.