I don't think that there is one particular statue called Christ in Marble. Over the centuries there have been very many statue's of Christ in all sort's of situations carved in the material marble. There is a particularly fine one here which was done in the year 1499AD.
.... I'm sorry to have to say that the "Ecce Homo" in Trafalgar Square seen here is not in marble at all, it is resin that has been given a finish to look something like marble. Ecce Homo -Once more Pilate went out and said to them, "Look, I am bringing him out to you, so that you may know that I find no guilt in him." So Jesus came out, wearing the crown of thorns and the purple cloak. And he said to them, "Behold the man" .......