Key Points:

Prime Minister Helen Clark has denied doing a U-turn on smacking, despite the National Party circulating past comments suggesting she does not support a ban.

Heln Clark is among 63 MPs expected to vote against an amendment put up by National MP Chester Borrows that would change Green MP Sue Bradford's bill and allow light smacking.

Ms Bradford's bill removes the defence of "reasonable force" for the "correction" of children.

It is in response to people using the defence to escape conviction for beating their children with riding crops, pieces of wood and other implements.

Opponents say the legislation would technically ban smacking and have dubbed it the "anti-smacking bill".

But the National Party today circulated a transcript of Miss Clark, speaking before the last election, saying she did not support a smacking ban.

Opponents have seized on the comments, accusing her of a U-turn.

In the 2005 exchange, on Radio Rhema, one of the bill's most ardent opponents, Family First spokesman Bob McCroskie, asked Helen Clark if she wanted to see smacking banned.

The Prime Minister replied: "Absolutely not. Well, I think you're trying to defy human nature".

But today she said her stance had not changed. She still did not support a smacking ban and did not believe that was what Ms Bradford's bill would achieve.

She said smacking was already illegal, as was all hitting.

But parents were currently able to defend assault charges under the statutory defence of "reasonable force".

Ms Bradford's bill would remove that defence for the purpose of correction, meaning people could no longer beat children with riding crops and other implements and get away with it.

Ms Bradford's bill did not explicitly ban smacking, she told reporters.

"This is not a bill which outlaws smacking.

"The Act now, the law now, says it is a crime to hit anybody, but the reality is our police are sensible people.

"They do not trot a harassed mother in a supermarket off to court. They will not under Sue Bradford's change. What they will be able to do is successfully prosecute people who beat children."

Ms Bradford also told reporters the bill did not explicitly ban smacking and did not make it a specific offence.

Hitting anyone was already an offence.

However, police did not prosecute parents for smacking children under the current framework and she did not think that would change even though she acknowledged a legal defence would have been removed.

Ms Bradford said she was confident she still had the numbers to pass the bill, despite opponents successfully delaying its passage last night.

Opponents mustered enough speakers to prolong the committee stage debate until Parliament adjourned at 10pm without Mr Borrows' amendment being put to the vote.

Ms Bradford has enough votes to defeat the amendment but National MPs now have several weeks to try to turn that around.

The amendment is likely to be put to the vote in two weeks' time, but it will not come up for its final third reading until after the Easter recess.

MPs against the bill dominated the debating chamber last night, condemning the legislation as "home invasion by the State" and saying it has the potential to create huge problems for the police and welfare authorities.

MPs said they had conducted surveys in their electorates, which had shown up to 85 per cent of their constituents did not want the bill to become law.