Someone spat at me, so I punched them, advice?

Worst case scenario you get punished.

Best case the policeman gives the other guy a slap on the wrist and tells him he was naughty. And same for you.

Not enough violence going on in this situation for anything more to happen.

Think you have a VERY strong ground for self-defense - and from your story it wouldn't be in the public interest to prosecute you anyway.

Sorry to hear you have had to deal with somebody who is obviously a complete nutcase.

I was bullied in school, but that was past me.

I saw this person as I was walking out of the store (he and his friends use to bully me at school and make my life hell) and he started to hurl abusive language at me and then as I continued walking he spat at me and when I turned around and ask why he done that he started to confront me even more and he was ready to punch me so I had punched him first at that point as I felt in danger and to avoid any further altercations, I walked away.

Someone suggested I make a police report (which I did) and they booked me into an appointment for next week to 'note' down what had happened.

Thinking about that, I shouldn't have made that report as now I could be 'punished' for hitting him? Correct?

Spitting is assault, but punching someone for spitting at you is not reasonable force, and it is not self-defence. If you get spat on, you walk away even if they spit at you again; it is not justified to punch them.