National MP Maureen Pugh says 'very important' for National Party caucus to unite behind a single leader

National MP Christopher Luxon appears to be ahead by a small margin in the race to become the next leader of the National Party - but it's still too close to call. 

Newshub has been told from within the caucus that Judith Collins has corralled her small number of loyal supporters into backing Luxon over her nemesis Simon Bridges. 

List MP Maureen Pugh, who Bridges once called "f***ing useless", is among them. 

Newshub caught up with Pugh on her way into Parliament on Monday afternoon, and while she wouldn't say which way she was planning to vote at Tuesday's decider caucus meeting, she did say it was "very important" for the caucus to get behind a single leader - but wouldn't say if that leader was Luxon.

The National Party leadership vote takes place at 3pm on Tuesday.