Yes, I agree that I have had some great advice and wonderful support so I thank you all for taking the time and trouble to care. 
I spoke to the teacher who was allegedly told him he could leave and she put me in the picture of how it was said. It was in a classroom situation, addressing all the class, not him as an individual and as he had made out. She listened to my side of what has been going on and as his pastoral tutor, said that she would find him and talk to him. So I will see what happens there as she hasn't done this yet.
I also spoke to the head and the upshot is a meeting with him, my son, his maths teacher and myself in two weeks. He is forecast to fail his AS level in maths so why is he carrying on with it as he won't be able to do his A level if he doesn't pass his AS? And I was the one to call the meeting. Surely this should have been done by the school if they know he is spending time studying a subject they have predicted a fail in? Is it just me?
Anyway, that is where I am at. Apart from him just having a paddy when I asked him to stop swearing again, took a swipe at my laptop and then went to his room as I had told him to go upstairs. He certainly is pushing the boundaries and stomping his feet. Maybe it's my fault for having been lenient in the past with both my kids. Maybe when I have then said something they are objecting venomously because they are not used to me putting my foot down. And I thought I was picking my arguments. What's the use in shouting about a tattoo or piercing when if they lie or deceive or are abusive it is more of a problem to be tackled? Have they become like this because they are finding more serious things to shock me with and get a reaction? They have always had my attention, they do not need to get "bad" attention. Or is this how children work to break away from their parents? Psychology is intriguing. 