I would send him a nice letter explaining the ownership and perhaps enclosing a copy of the deeds. Send it by hand.
If this elicits no response, then repeat the letter but add that you don't want to go to the time and expense of solicitors etc. Have this delivered by recorded delivery.
If that doesn't work, then consult a solicitor.
DO NOT just block him in. If you did and he called the police, you would be the one in the wrong. You also do not want to fall out with your neighbour as a standard question when selling your house is have you had complaints. If you have then you will automatically devalue your house.