Technically, in the UK at least, you're within your legal rights to strike first providing that you were placed in fear of an immediate physical attack and you use reasonable force. However, I do see what you mean in that practically speaking you may have problems convincing the police of your defensive action. It doesn't help that many police officers aren't aware of the actual legal situation. So I would add to the excellent points you made that its a good idea for people to actually learn the legal position (preferably word for word) and, should you be called upon to make a statement to the police, phrase it in those terms.