Last Saturday's vote showed a sharp split among his party's traditional supporters.

ECONOMIST: Australia mislays its republic

Many observers see Pierce's role in the three-way race as that of a spoiler, saying he may split the anti-Kim vote and enable Kim and his core supporters to win the primary.

CNN: Kim Escapes Prison Sentence But Still Faces Ethics Panel

Labour leader Ed Miliband is campaigning for a yes vote in the referendum but his party is split on the issue.

BBC: Q&A: Alternative vote referendum