Hello again and thanks for the extra info.
As the donor is not named on the birth certificate, that means that he does not have parental reposnsibilty - which although largely symbolic would have meant that you would have been obliged to get his consent or permission from the court on major decisions in your boy's life, like changing his name, or emmigrating, and also he would have had the right to be kept informed of your boy's education progress and health issues.
However, as the agreement made was not via a fertility clinic, it means that the arrangement was not regulated by the HFEA rules, which means that the donor WILL be treated as the legal father, which gives him the right to apply under section 8 of the Children Act 1989 for a child arrangements order for contact with your boy.
The question is how will the court treat his application for contact. The court must decide any issue concerning children according to what is best for that particular child.
Unfortunately for you, the court does place great value on fathers having contact with their children, unless there is very good reason why that should not happen. You could use the fact that his behaviour was threatening as a reason why he should not have contact - but that may not be enough for the court to agree that he should have no contact at all - the court could order contact at a contact centre eg for an hour a month.
At a very minimum, the court is likely to order that he should have the contact that you offered ie indirect contact of annual photos & udates, but the ocurt might order mores frequent indirect contact, or even face-to-face contact - but that could be supervised - eg at a contact centre.
I'm afraid there are cases where donors were sucessful in getting the court to make a contact order in their favour.
If contact centre contact was ordered, and then he did not keep to the order eg he missed sessions or turned up late or left early or did not behave appropriately within the session, or continued to be threatening to you, then you could take the case back to court to ask for the order to be revoked.
Given the age of your son, it's unlikely that anyone other than you could supervise the donor's contact with your boy (unsupervised contact is very unlikely to be ordered, given that your boy is still a baby and doesn't know this man at all). If the relationship with the donor is such that to be in the same room as him would be very stressful to you, and your baby would pick up on your distress, and become distressed as well, that might be an argument that you could use against the donor having any face-to-face contact with your son.
Either you or he could start the court process, for which you need form C100, here:-
However, going to court is stressful, time-consuming and expensive, to be avoided if at all possible. The family court anyway now requires the parties to have attempted mediation before it will consider an application to court, so here's where to find a local family mediation service:-
There is a specialist fertilty law firm which could give you expert advice here:
but if that is not local to you, you can find a specialist family law solicitor here:
I hope this helps and I wish you the best of luck.
Thanks and best wishes...