Being Harrassed by someone with 2 convictions already.?

This person has twice been to my block of flats. The first time I was away, the second time he called up on the intercom I told him that if he did not go I would call the police. He left straight away. Then last Friday he walked into the reception at my work. I was there with a security guard. I told him to go away and he did. My concern is that eventually my luck will run out and he will corner me when no one else is around. Last time this happened he assaulted the person in there own home. This has been going on for over 2 years now and I have done nothing to discourage his attempts. I have not attempted to make any contact with him so he must know I am not interested in anything he has to say. I just wondered if the police would be willing to have a word with him before thing get out of hand. He does have after all alreadyhave a convition for harasment. And as they say Leopards never change there spots. Prevention is better than cure as they say.