Thanks Adam

I was a little puzzled as I couldn't find this property anywhere. The fact is that the default code doesn't display the property e.g.
<CE:Editor id="NewsItemBody" EditorWysiwygModeCss="../example.css" runat="server" ></CE:Editor>

So I had to put EncodeHiddenValue="false" there myself and ensure it was set to false e.g.
<CE:Editor id="NewsItemBody" EditorWysiwygModeCss="../example.css" EncodeHiddenValue="false"  runat="server" ></CE:Editor>

However it requires that ValidateRequest="false" be added to the page directive like so (or your page will generate an error):
<%@ Page Language="C#" ContentType="text/html" ResponseEncoding="UTF-8" ValidateRequest="false" %>

W