If the socket no longer needs to be there then I'd remove it, because this example illustrates folk will always be tempted to plug random stuff into unused outlets, even in an airing cupboard. In my own house, the washing machine is in the airing cupboard at the bottom of the bath. It was originally plugged into a socket in there, and I was happy to leave it like that until it was time for a new one. At that point I replaced the socket with a flex outlet plate and added a FCU on the outside of the bathroom wall. I also reversed the cupboard door so it is impossible to touch anything in the cupboard whilst in the bath. Some may argue that it would have been fine as it was, but I think I made sensible improvements. We certainly have nowhere else to put the washer in the house, and since the dirty linen ends up in the bathroom anyway, I like having it in there!
