Should expelled list MPs have to resign?

Brendan Horan's expulsion from the New Zealand First caucus raised an interesting question - should list MPs who are expelled from their political parties have to resign from parliament? We conducted a poll to find out what New Zealanders thought about this issue.

As several commentators have pointed out, the Brendan Horan situation is, on the face of it, different from the classic party-hopping scenario. Whereas several of the early cases of party-hopping under MMP involved MPs choosing to leave the parties they were elected to represent, Brendan Horan was initially expelled from the New Zealand First caucus against his will. The poll results suggest that New Zealanders aren't particularly fussed about this distinction.

70% of New Zealanders believe that list MPs who are expelled from their parties should have to resign from parliament.
16% think that they should not have to do so, while 14% are unsure.

Brendan Horan's situation involves allegations of inappropriate behaviour, and it would be interesting to see whether the public would be more sympathetic if a list MP was seen to be leaving their party on principle. On the other hand, I haven't been able to find a single list MP who has either left their party or been expelled from it who succeeded in returning to parliament at the next election (including those who set up new parties to try) - that includes several who claimed that they were leaving on principle because of differences with their party. Here are the names I've been able to come up with:

Alamein Kopu (resigned from the Alliance in 1997, founded Mana Wahine, lost in 1999)
Frank Grover (resigned from the Alliance in 1998, switched to Christian Heritage, lost in 1999)
Jack Elder, Peter McCardle, Ann Batten and Deborah Morris (all left NZ First on the break up of the coalition with National in 1998 - Batten joined Mauri Pacific but failed to be elected in 1999 while the others did not stand)
Donna Awatere Huata (expelled from the ACT party in 2003, forced to leave parliament after a Supreme Court decision in 2004 because of the party-hopping legislation then in place)
Gordon Copeland (resigned from United Future in 2007 over the anti-smacking legislation, founded the Kiwi Party, lost in 2008)

Are there any list MPs I've missed? I wasn't sure if to count the Alliance from 2002, as they only officially split after the election, and I left out David Garrett (ACT) as he left parliament a few days after being thrown out of his party.

Electorate MPs who switched parties on apparent principle have often done better - Tariana Turia's managed to keep a large majority in her electorate despite switching from Labour to the Maori Party, and Hone Harawira held his seat in both a by-election and the 2011 general election.

The rundown of 'party-hopping' list MPs above has some interesting aspects:

All eight came from minor parties - none came from National or Labour, despite both parties having significant numbers of list MPs at most elections.
The only minor party with list MPs not appearing is the Greens (the Maori Party and Mana have never had list MPs).
Since 1999, only one list MP has resigned from his party to stand for another - compared with six between 1996 and 1999. The other two were removed from their parties against their will.
I imagine only Donna Awatere-Huata could have been described as a household name before they resigned - most of those who resigned on apparent principle would have barely been known to most New Zealanders before they switched.

So, what do you think? Should list MPs have to resign if they are thrown out of their parties, even if they continue to vote for the same way as their old party in parliament? Are there any circumstances when it might be ok for a list MP to stay in parliament?

If you're interested in the full report, including demographic breakdowns, you can see it at http://umr.co.nz/updates/most-nzers-think-expelled-list-mps-should-resign.

We're also running a related poll on our Facebook site (http://www.facebook.com/sayitnz) - Should the law force MPs to leave their parties to resign from parliament or face a by-election?