If you have identified your neighbour as the owner of the vehicle, discuss the problem with him first in order to explain the situation and find a compromise. If the situation persists, the answer will depend on the situation and the parking place. The articles of the Highway Code that can be applied are accessible via the following link:
Parking Regulation Please contact the gendarmerie brigade or the police station, or even the municipal police, of your town to obtain more information and have the problem solved.