NZ First MP Winston Peters has decided to stand for his home electorate of Northland in the by-election.

NZ First leader Winston Peters has confirmed he is standing in the Northland by-election.

The Northland-born veteran hinted at a tilt at the seat in a speech to Parliament on February 10 when he told the electorate "hang on, help is on its way and the campaign will start soon".

At a media conference at Parliament this afternoon, Peters said his campaign started today.

David White Science and innovation minister Steven Joyce speaking to the media on winston Peters runnng in Northland

He declared the seat "winnable", because the economic and social circumstances in the area were "being neglected and ignored".

He said that standing in the by-election was not an easy decision, but he had a long held concern for "Northland's forgotten people".

"Victory here won't change the government but it will change the way they think," he said.

National had forgotten Northland for years, and the region was stagnating, Peters said.



NZ First was the underdog, but Peters said he'd had "countless" phone calls asking him to stand.



"I start with the good fortune of them knowing me."

Peters said there had been no deal with the Labour Party to lessen their campaigning efforts to give him an advantage, and he was "putting it all on the line" for the electorate.

Northland needed a real voice that could hit the ground running, he said.

The vacancy was created by the resignation of Northland MP Mike Sabin for personal reasons.

Sabin won the seat for National with a majority of more than 9000 at the September general election.

NZ First did not stand an MP in the seat, but gained 4546 party votes there.

Peters denied Northland was a safe National seat, saying the party lost there in 1963, and he believed he could win it.

"We're up to it, we're match-fit," he said.

NZ First would get another list MP if Peters won Northland, but he denied that was the reason he was standing.

The party got 11 MPs at the general election. Invercargill woman Ria Bond was 12 on the NZ First list.

The call has gone out for the $52,000 needed to fund the campaign.

National has shortlisted five nominees - Grant McCallum, Mita Harris, Matt King, Mark Osborne and Karen Rolleston - and will choose their candidate a final selection meeting tomorrow.

Labour has confirmed Willow-Jean Prime as its candidate, and the Act Party will stand Whangarei orchardist Robin Grieve.

Labour leader Andrew Little said he had not considered standing Prime aside to allow Peters an advantage, and would not do so.

"We're backing her 100 per cent."

Little said National should not take the seat for granted, and he sensed people in the region were annoyed Sabin had let them down.

The seat was "anyone's game," and Prime was well known in Northland as a Far North District councillor, Little said.

The Green Party and the Maori Party are not standing candidates.

The by-election will take place on March 28. Nominations close on March 3 at midday.

IF PETERS WINS...

If Peters wins then the proportionality of Parliament would change.

Under the rules of MMP if he wins he could resign as a list MP and the next candidate on NZ First's list would be elected.

So NZ First would continue to have the 11 list MPs it was entitled to because of its party vote at the 2014 election plus it would have Winston Peters as a 12th - electorate only - MP, the Electoral Commission has confirmed.

However, National would not gain another list MP to compensate for the loss of Sabin.

The issue was covered in a 2012 report into the MMP system.

It noted that if the party that won a seat at a general election lost a by-election the proportionality of Parliament might alter "and even change the balance of power".

But the current system of MMP does not guarantee a proportionally-balanced Parliament for the entire three-year parliamentary term anyway, since an MP could break away to form another party or merge parties, or an MP may be expelled.

The loss of Northland would not threaten the Government's survival, but it could make it harder to govern.

National had 60 seats in the 121-seat Parliament before Sabin resigned. It is supported by ACT's David Seymour, UnitedFuture's Peter Dunne and the two Maori Party MPs. which gave it 64 votes on crucial confidence motions.

If it lost one seat to NZ First it could still command a majority by 63-58.

But it could no longer rely on any one of its supporting MPs to give it the necessary 61 votes to pass laws. For instance, if the Maori Party was not in favour of a law change, John Key would need both Dunne and Seymour's support to pass a law.

Interestingly, if Peters won Northland there would be a majority - 61-60 - opposed to sending troops to Iraq, though no vote is needed to approve the deployment.