It's called trespass. You call the police, you say that a man is trespassing on your property, you have asked him to leave repeatedly, you have told him he is trespassing (this is important, called notice of trespass) and you are afraid to take further action because he might become violent.
If the guy has no legal right to be on the property then he is trespassing. It gets cloudy when he has been a resident, but you have dealt with that with an eviction order. Once the police are there if they balk due to the guy claiming he lives there or whatever, you show them the eviction order. If they still balk, get their badge numbers.
Trespass to Property Act
Nice to figure out where I stand and how to go about it.!!