On the plus side.
By chance I was checking sedo's UK listings for names that I might be interested in and found one of my names listed - following the advice above I emailed sedo and asked them to remove the name as it was mine, was not listed by me and was not for sale. I am pleased to say that I received an email confirmation within 12 hours that the name had been removed from the listing and on checking it had been removed.

On the negative side
In light of this thread I now feel that I'm going to have to check all of my names just to be sure that none of them are listed! I don't really want to have to do this! I know that I haven't listed any with Sedo but I have had demonstrated to me that that stands for nothing - the burden of responsibility has been put upon me to ensure that names I own are not listed and I am uncomfortable about that.
Is someone somewhere offering my car for sale ... or my house?
I feel a change is needed.