I just want to thank everyone for the interesting dicussion that this question has generated and for the contributions that have been given by all.
In light of what has been written, would it be fair to say that the Theravada understanding is that while cultivating Metta can help supress the three poisons (as well as other practices targeting Attachment and Ignorance), only Panna, via Vipassana into the four noble truths, three characteristics ect. can elimate them entirley and so lead to Nibbana?
"If beings knew, as I know, the results of giving & sharing, they would not eat without having given, nor would the stain of miserliness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared."