Both in the UK and the US, you can defend yourself against a reasonable belief you're immediately going to be attacked. Quoting a random google'd legal page:
That can be pulling back a punch, or picking up a knife or an aggressive physical move. If I sit in an armchair and say "I'm gunno slap your face" I haven't handed you the right to break a chair over my head.
Even in the various cases where battered women have killed/burnt alive their sleeping husbands, self-defense is not a workable plea as there was no imminent danger - self-defense has to be an act to avert a danger *now*.
(My understanding of this law comes from the UK, although all the web references I found in a couple of minutes of looking were from the US).
Ok so it's how I thought it was. I remember situations with cops which included the matter of a verbal threat. The people who were feeling threatened were basically told words alone mean nothing...which was why I was suprised at the idea that verbal threats could constitute grounds for self-defense. "I'm going to kill you" isn't enough.