Morning all. 
Charlotte, agree with fool, he really is very abusive. In Lundy, there is a description of an abusive situation that really, really mirrors yours, about a man deliberately making everyone late but then it gets turned around onto his wife. He is doing it deliberately to control, manipulate and upset you. That's abusive. I know you are doubting it, but it is, and he can't be allowed to carry on treating you like that, he has no respect. And the driving thing, raging at other drivers - NSDH did that, I hated it, I felt it was symptomatic of his lack of respect for me that he thought he was so always in the right while driving, and anyone making the teeniest mistake got called a 'fucking bitch' really nastily. Unnecessary. Plus it scared and upset me. But he didn't care. That's not a loving relationship.
And you know what Charlotte? Even if he isn't abusive (although he is) - it doesn't matter what it's labelled. If you are deeply unhappy and feel it's not a loving, secure, happy, nurturing relationship for both you and the kids, you are more than entitled to leave, end it, separate, get out, whatever. Just because you feel it's not as bad as other people's experiences, doesn't mean you should still have to suffer it. You are a good person, you deserve to be loved and happy. 
trying, that's awful, poor DD. NSDH did that 'head clipping' to my DS1 a few times in the early days, as a punishment/telling off, seemed to think it was acceptable (no!), I set him straight. However, he's still 'rough' with him sometimes. And I've been clipped by NSDH like that too (while pregnant), it's awful, and, as you say, really demeaning - it wasn't the pain of it that brought tears to my eyes, but the shock of it and the shame of being treated like a naughty child.
Yes, you are completely right to leave. On that basis, and on the basis of everything else. And also because you want to. That's all. You get to choose whether you go or not, because it's up to you. I agree, get another lawyer. One that I spoke to was an DA specialist, it was on their website that they dealt with that, and the lawyer I spoke to had dealt with many cases before and was very knowledgable. You cannot brush it under the carpet. It's the whole reason for you leaving. It affects his contact with the kids too. I agree with everything fool said (as usual
), get his treatment of DD on record somewhere, maybe a word with her teacher to see if they have noticed a difference in her behaviour, or speak to your health visitor if SS seems too scary.