Revealed: The big reason Judith Collins isn't running for the leadership this time

Judith Collins says there's a simple reason why she's not running for the National Party leadership - she'd lose.

The party will today decide whether to stick with incumbent Simon Bridges - whose leadership has seen the party plummet in the polls - or take a chance on the relatively unknown Todd Muller, who wants to take over the reins.

There are reports Rodney MP Mark Mitchell - a former private security contractor and policeman - may also throw his hat in the ring. 

Collins has twice contested the leadership before, losing the first time to Sir Bill English and the second to Bridges. Asked on The AM Show if she'd make a last-minute run, she was adamant.

"No. I'm not interested. I do not have sufficient support in the caucus to be the leader. I have some very great support in the caucus, but I do not have sufficient [support]. 

"I'm not going to waste our time going in an election year with only three-and-a-bit months to the election worrying about myself. The fact is we have a job to do, and I want us to get on and do that job."

Collins has been in Parliament for 18 years - as long as Bridges and Muller combined - and was ranked 16th on the party list in 2017, the same as Muller is now. Collins is now ranked fourth, but says even if Bridges and his deputy Paula Bennett are deposed, she wouldn't want the deputy role.

"I'm not interested in being the deputy for anybody... I do not want it. If someone offered it, no."

Collins with Labour's Willie Jackson on The AM Show.
Collins with Labour's Willie Jackson on The AM Show. Photo credit: The AM Show

Whilst that might sound like something somebody who wants the leadership might say, Collins says she's happy just "being the MP for Papakura". 

Having Collins' support is likely to be a necessity for the winning candidate, with the vote expected to be close. She wouldn't say who she plans to vote for - even refusing to answer which candidate she'd rather go out on the town with, trust to look after her pets or never see again. 

"I think that either candidate has excellent qualities... and they are both capable of doing a lot more than some people might think."

The vote is expected to take place early Friday afternoon. Whoever wins will have the big job of dragging National back into contention - two polls this week have had them more than 25 percent behind Labour.