A senior National party figure is accused of attempting to derail a candidate for the Auckland Central seat with a late-night call to talkback radio.

Nuwanthie Samarakone's campaign for the seat - which will be decided tonight - has been rocked by controversy recently.

Newshub alleged the man, who called himself Merv on a call with Marcus Lush on Newstalk ZB last Monday, was actually party board member Roger Bridge.

The Herald understands the person called from Bridge's phone. Bridge could not be reached when contacted by the Herald tonight, but he denied he was the caller when questioned outside Parliament.

A spokesman for National leader Judith Collins said she had no comment.

Merv told Lush he was in Manurewa and had planned to vote for Samarakone for the local seat before she decided to run for Auckland Central.

The Auckland Central seat became available after the resignation of former National Party deputy leader Nikki Kaye last month.

Claiming to be confused about how Samarakone is running in Manurewa and Auckland Central, Merv decided to call Lush just before midnight last Monday.

"I'm a bit confused because there's billboards all over the place with this 'Nuwi' girl and then I understand that she's also standing in Auckland Central," he said.

"Can you have a candidate in one electorate also standing for another?

"She's already standing in Manurewa and I was ready to vote for her but now I understand that she's going over to Auckland Central - I'm confused."

He also raised questions around a photograph that had been spread around the National Party of Samarakone in a fitness leotard.

Samarakone told Auckland Central delegates in an email last week the photo was from when she was competing "in the fitness realm" a few years ago.

She has also said she'd been targeted by incorrect claims she used to be a stripper.

She vehemently denied the allegations and hired Julian Miles, QC, to fight the "damaging, malicious and untrue campaign".