Simon Bridges' supporters accuse Judith Collins of set-up, possible caucus challenge underway

This is mayhem. Pure unbridled political mayhem.

Judith Collins has demoted her challenger-in-chief Simon Bridges after a week of bad polling and political agitation.

Newshub understands the complaint relates to something that happened five years ago. A group of National MPs including Simon Bridges, Jami-Lee Ross and Todd McClay were together with Waitaki MP Jacqui Dean. The allegation is that something was said to her of a sexual nature that Dean found humiliating and designed to dominate.

The complaint was kicked up to then-National leader Bill English who tonight refused to comment to Newshub.

Bridges isn't commenting but his supporters say this is a set-up - that the anger in the party is directed at Collins.

Collins is holding a press conference on Thursday morning at 10am. We understand Jacqui Dean is planning to attend.

It doesn't sound like she's planning on laying a complaint with police but in her statement, Collins says the comments caused ongoing distress.

In another twist, we understand the National Party board is meeting urgently. Collins says she had unanimous support from the board to demote Simon Bridges but other National Party sources say there was no vote.

Parliament is sitting right now - National MPs are in there.

Other MPs are meeting in offices up on the party's third floor. It is all on here.

Newshub understands the caucus is trying to meet now - possibly trying to mount a challenge - it could come tonight or tomorrow.

It is very hard to see where this will go because right in the National Party it is chaos.