1. Dear Jill, the person named in the defamatory post can force whoever painted the wall to remove it. However, unless the person who owned the wall painted on it, the owner of the wall cannot be forced to remove the paint. In essence the owner of the wall is a neutral third party whose property has been defaced by the painting on it. However, just because they own the wall, this does not give rise to a liability to remove everything written on it, if the writing offends a person. If you are the person about whom the wall painting has mentioned a name, then I would suggest that you either remove the paint or else get the permission of the owner of the wall to paint over what is painted there in an appropriate colour which hides the paint.
2. However, there is no point in suing the owner of the wall as they don't have a liability in law to the person who is mentioned in the paint written on the wall. It is only the person who wrote the paint on the wall who bears a liability to the person mentioned, in defamation, malicious falsehood or negligent misstatement. The owner is an innocent party and liability cannot be imposed merely because someone chose their wall upon which to write a defamatory statement.
3. The position would be different if the owner of the wall painted the writing on it. Then the owner of the wall would bear a liability to the person mentioned as they wrote the paint on the wall and the owner would then be liable to be sued in defamation, malicious falsehood and negligent misstatement. They would also be subject to an injunction to remove it.
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