What makes a conscience vote?

It seems a conscience vote isn't always what it appears.

Conservative Party leader Colin Craig says MPs should always align their vote to the wishes of their electorate, regardless of whether the matter is subject to a conscience vote.

It follows a survey he's carried out which he says shows most Helensville residents aren't in favour of the Prime Minister's support of the same-sex marriage bill.

Massey University political scientist Claire Robinson says generally, a conscience vote is the MP's personal view.

"In some instances the party will tell them what they should be voting, which direction they should be voting, and it often comes down to how the party perceives the issue in the public arena."

She says sometimes MPs are told which way to vote on a conscience vote, but that wasn't the case for the gay marriage bill.

"I suspect for the alcohol age they were probably given more of a direction about how to vote, but for the gay marriage it seems to be based on their own personal views."

Wairarapa MP John Hayes was one MP who made it clear he voted against the Marriage Amendment Bill, after canvassing his electorate.