If you punch someone and hurt them, you’d be okay provided you used ‘reasonable force’ - and that’s up to a jury to decide.
“If there has been an attack so that self defence is reasonably necessary, it will be recognised that a person defending himself cannot weigh to a nicety the exact measure of his defensive action. If the jury thought that that in a moment of unexpected anguish a person attacked had only done what he honestly and instinctively thought necessary, that would be the most potent evidence that only reasonable defensive action had been taken …”
If someone attacked you, protecting yourself in the moment is more important than potentially getting nicked later on. Hit them.
I thought aikido was kind of pointless? Saw some demos at uni and it looked too choreographed and compliant to be useful. Happy to be shown YouTube clips of Steven Seagal aikido-ing people in the face to prove otherwise.