The selection of National's candidate for the safe Rodney seat has been delayed amid bitter infighting, with frontrunners Brent Robinson and Scott Simpson said to be tarnished by claims of attempts to slant the selection process in their favour.

Delegates were to have met this week to select the candidate to replace Lockwood Smith from a shortlist of five - Mark Mitchell, John Kirikiri, Christopher Penk, Mr Robinson and Mr Simpson.

However, that has been put back to March 14 and it is understood that is at least partly because of concerns that Mr Robinson's supporters tried to "stack" the selection committee in his favour by signing up new members to his Wainui branch.

It is also understood a number of those signed up recently to Wainui should, according to party rules, have been registered to other branches because of where they live.

National's hierarchy has decided to formalise branch boundaries within the electorate, a move that is likely to see members reallocated from Wainui to other branches.

The Herald is also aware of concerns around the criteria by which National's northern regional chairman, Alan Towers, chose delegates to sit on the selection panel.

A party insider and political blogger Cameron Slater claim Mr Towers had appointed delegates favourable to Mr Simpson - or was intending to.

With both frontrunners now perceived to have indulged in "dirty pool", the party insider said the way was now clear for one of the other candidates to come through.

Strong potential contenders include Mr Mitchell, a former policeman, and Mr Kirikiri, the district's former deputy mayor whose key strength is said to be his strong relationships within an electorate that is regarded as very parochial.

Another party stalwart also said the competition was now far more open.

"People want this to be a fair contest and they don't want to see a few people abusing the rules, so I think there's an element to that."

Dr Smith, who is to move to the party list for this year's election, held Rodney with a majority of more than 15,000 votes in 2008, and whoever wins selection is virtually guaranteed a seat in Parliament.

Neither electorate chairman Cehill Pienaar nor party president Peter Goodfellow would acknowledge that allegations of committee stacking were behind the decision to postpone the selection meeting.

Mr Goodfellow said the party hierarchy had found electorate records of where members lived and which branch they were in "haven't been as accurate as we would have liked".

Mr Goodfellow said he understood Mr Towers was reconsidering how he would appoint delegates to the selection committee.

This was because of "the criticism he's facing that the way in which he's exercised his discretion hasn't generally been what you'd expect".

This week, however, Mr Towers dismissed the allegations about his selections as "ridiculous".

The only changes he was making in terms of appointing the 15 delegates needed to make up the quorum of 60 for the selection panel would be to reflect changes to the pool of potential delegates resulting from the reallocation of party members among the electorate's four branches.

Meanwhile, Mr Pienaar, who has come under fire because of his former role as leader of South Africa's Conservative Party in the early 1990s, has chosen to stand aside from the selection committee that will appoint the new candidate.

Asked about the prospects for a candidate other than Mr Robinson or Mr Simpson to now take the nomination, Mr Pienaar quoted an Afrikaans saying: "When two dogs fight, the third goes away with the bone."