ACT's David Seymour believes the opposition has drifted too far to the left - and it's dragged the party down.

Seymour has fired back at Labour after a full week of scrutiny and calls to resign following his letter advocating for Philip Polkinghorne and the Land Rover on Parliament's steps incident. 

He says Labour used to stand for equality and democracy and fairness, but they've gone adrift over the years.

"They've given up on the idea of one person, one vote. If you take Willie Jackson, one of their most prominent ministers, who says - oh democracy has changed now, one person, one vote's not that important . Actually, one person, one vote is the whole point of democracy."

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