(mind you, i don't expect either of these two to be it, because the terms are probably confined to Aus, because of the preferential voting system; see here and here. Just think of the fun you'd have if you got preferential voting in the UK. woot.)

Darren] A wasted vote? Close, but no cigar
CdM] a transferable vote? Almost certainly not
all] postal vote? As close as the other close guesses
flerdle] An informal vote? Possibly
flerdle] A donkey vote? No
So that's what a donkey vote is. I always thought it was the loyal vote for a long-standing member - because healw-healw-healways gets elected sorrysorrysorry
Raak - A spoiled vote? Almost certainly not

[Irouléguy] That deserves a thwap. *thwap*

goodness, how many are there?

flerdle] *thwap* Ouch
flerdle] A casting vote? Almost certainly not.
goodness, how many are there? GOOD question

Tuj] A vote for a specific party? As close as anyone else has got, but no
Raak] A majority? No
Chalky] Does the answer contain the word 'vote'? GOOD question - No
Gusset Login] A proxy vote? Close, but no
Gusset Login] An illegal vote? Almost certainly not
Gusset Login] A Pop Idol vote? Definitely not
One of the guesses above contains the answer

flerdle - Protest? No
Normal service may be interrupted for some time, as I'm off out canvassing, knocking up, etc and I'm not quite sure when I'll be back. Clues
1) The answer could be in number 10
2) The answer is in the next government