You will plead guilty on your first appearance at the magistrates hearing. This is called the plea and direction hearing. You may be able to avail yourself of the duty solitcitor who can advise you of the process. But essentially the earlier you plea, the more sorry you are, the smarter you dress and provided there weren't any aggravating circumstances and this is your first your punishment should be on the lower end o the scale. Expect a ban, a fine which wouldn't be too onerous and an opportunity to attend an awareness course. The ban willl be the most painful part of your punishment.