During the past three years, MPs have voted according to their conscience rather than on party lines on major social issues.

The debates on these matters were at times divisive and the numbers on occasion extremely close. For example, the vote to decriminalise prostitution was passed 60-59.

But this does not mean that MPs act entirely on their own. There are often pressures from their communities, and the voting patterns suggest that issues are decided on party lines.

With the conscience vote on the Civil Union Bill, Labour MPs Winnie Laban and Ashraf Choudhary chose not to vote on the first reading of the bill, rather than decide yes, no or abstain.

Dr Choudhary, born in Pakistan of Indian heritage, is New Zealand's first Muslim MP and, as a list MP, was also selected by Labour to be a representative of ethnic communities in Parliament.

Mana MP Ms Laban is a New Zealand-born Pacific Islander and confirmed she was lobbied by Pacific Island church communities from within her electorate to oppose the bill.

However she admits she switched her vote in favour of decriminalising prostitution at the last moment, despite the lobbying, after hearing an impassioned speech from fellow Labour MP Georgina Beyer.

Disgraced former Act MP Donna Awatere Huata was not in Parliament for all the conscience votes but did vote against decriminalising prostitution.

One of the first conscience votes of the new Parliament will be on Green MP Sue Bradford's proposal to outlaw parents arguing they used reasonable force in physically punishing a child.

How it works

MPs are freed from the usual obligation to vote according to party lines.

The conventional view is that MPs vote according to their own wisdom.

They do not have to second-guess what their electorate wants them to do.