"This time he has blocked in one of the centre users, who attends the local deaf support group. Their meeting finished half an hour ago, and the user, who is profoundly deaf may have to just wait here most of the day, and she is very distressed."

Until such time as effective action to deter the pest is taken, I think the centre needs to begin informing it's vulnerable visitors that there is a risk they may be stranded there for several hours when parking at the centre.