In what sense?
It is a criminal offence to spit at somebody - a man was sent to prison for 56 days for spitting at a traffic warden;
It is not an offence to spit in to your handkerchief;
It may be a breach of a byelaw to spit on buses or pavements
It should be an offence to spit on the pavement as many people seem to do - I saw girls doing it the other week which is even more disgusting somehow - it's disgusting enough when it's men.
I don't think there is a law against spitting per se (apart from byelaws). However, spitting at someone could be charged as an assault (which I suspect was the case with the case Ethel described) or criminal damage (there is a case where someone spat at a police officer's uniform and it was charged as CD) or potentially s5 POA - using threatening or insulting words of behavior.
I think it would really depend on the circumstances.
Like others who have posted here, I wish it was too!
At my youngest daughter's school we have had letters to parents asking them not to spit in the playground as it spreads disease and sets a bad example.
How bad is that when the teachers have to tell the parents how to behave!
When I was a boy there were signs on buses and in public spaces "No Spitting" but I think they were covered by bye laws or regulations. Spitting is disgusting but how do you police it?