National's worst week in office since the election was yesterday capped with a poll showing Labour has an unassailable lead in the Mt Albert byelection.

Labour may even increase its majority in the seat this weekend, which would be a big boost to the authority of new leader Phil Goff within the Labour Party.

Prime Minister John Key's day of campaigning in the electorate yesterday will be his last.

Mr Key and Mr Goff passed within metres of each other at Westfield St Lukes but the PM appeared determined to avoid his rival.

The pair have been engaged in a war over how to progress a complaint against former Internal Affairs Minister Richard Worth.

At one point yesterday, Labour activists followed Mr Key at St Lukes shouting, "Where is Dr Worth?" but he ignored them.

Mr Goff attributed Labour's commanding lead in last night's One News poll not to the Worth scandal but rather to the issue of the SH20 motorway extension through Mt Albert to Waterview, the Super City plans and the campaign run by National's Melissa Lee.

Mr Key also believes the fallout from Dr Worth's resignation has nothing to do with the poll. "I think people will see that this is a question of an individual member of Parliament's character and will see it less as a party affiliation. But that said, our preference would be that we weren't engaged in this episode at this time."

The best that National can hope for is that the loss in Mt Albert is not too humiliating and that Greens co-leader Russel Norman does not push it into third place.

Mr Goff is worried, however, that the huge gap will lead to complacency among Labour voters, who will think it's a done deal. "A low voting turnout is a real risk given the gap that is revealed in that poll and I don't think the result on the day will be anywhere near as spectacular as what that poll suggests."

Mr Key said that National's winning Mt Albert for the first time "was always going to be an uphill battle".

Mr Key updated the National Party board yesterday on why he had sought the resignation of Dr Worth on Tuesday night, but he is still not saying why publicly.

He said it was not a special meeting. And there was no talk of expelling Dr Worth.

Dr Worth is facing a police inquiry after a Korean businesswoman complained about an alleged sexual encounter in a Wellington hotel.

Whether the National caucus moves against Dr Worth may rest more on a complaint of harassment from an Indian woman in Auckland. She says she received vulgar messages from Dr Worth by text and telephone - allegations he adamantly denied when confronted about them in May.

Mr Key yesterday reiterated his willingness to meet this woman, but said she would first have to show the messages to his chief of staff, Wayne Eagleson.

Any proof she provided "would cast a very interesting light on the future of Richard Worth's parliamentary career".

Mr Goff advised the woman - a Labour Party member - to agree to meet only Mr Key, on the basis that he had said in a radio interview last Friday that he would rearrange his diary to see her if she brought the texts.

* Electorate vote
One News poll:

David Shearer, Labour, 59 per cent.
Melissa Lee, National, 21 per cent.
Russel Norman, Greens, 15 per cent.
John Boscawen Act, 3.3 per cent.

Last election:

Helen Clark, Labour, 59.29 per cent.
Ravi Musuku, National, 28.84 per cent.
Jon Carapiet, Greens, 5.94 per cent.
Kathleen McCabe, Act, 4.09 per cent.