I left my ex when my son was 4 month old he is now nearly 3, at first he was collecting my son for a visit 2 days a week which he dropped down to one day then none. He was mentally abusive when we were together and when we did split he was turning up at my house at all times through night and shouting and screaming at me, I was and still am scared of him. I can count on one hand how many times he has seen my son in the past 2 year as he is so unreliable. The CSA decided that he had to pay me £2.50 a week which he stopped and I haven't received this for approx 8mth even though he has been working. My son is happy enough with out him and doesn't even know who he is. When all of a sudden out of the blue he has turned up again making his usual threats and demanding to see my son. I know he is named on the birth certificate but he hasn't help raise him finacially and he has been unreliable before and I am sure he will be again. What rights does he have to see him??

He has the same rights you do. Even though he has been absent all this time, his legal rights can not be diminished. Maybe you could work out a court order together. If not, he could sue for partial custody or visitation, and win.