"They should never have had the investigation in the first place. These are figures that were going to be released anyway," said Mr Trotter.

"This is one of those rare moments when it's a cock-up and a conspiracy," added Trish Sherson, former ACT press secretary, wondering why the investigation will look as far back as February.

"Bridges handled it perfectly [on] day one. When those expenses were leaked he came out and said, 'Hey - I was doing my job.' It didn't seem to have anywhere to go, the story died pretty quickly, and then [came] the whole decision around going after who leaked it. That's just taken on a whole life of its own."

Mr Bridges told The AM Show in August it's important to find out who's behind the leak so "Members of Parliament to have a confidence about what happens with this sort of stuff" and "so the Opposition can do its job, so parliamentary democracy ultimately is safeguarded".

But Ms Sherson said there's no public good in finding out who leaked the expenses, and it's not a good look for National to be spending taxpayer money investigating the matter.

Mr Trotter said looking at communications as far back as February suggests the investigation is covering more ground that just who leaked the expenses, and that it's becoming clear National chose the wrong leader after Bill English stepped down.

"They have sent a boy to do a man's job... I cannot for the life of me understand why you would do this to yourself."

Spill on the cards?



Mr Trotter said Mr Bridges' days could be numbered, with hints of a plot to roll him forming behind the scenes.

"When you see pieces on the board moving about with this sort of speed, obviously there are things happening which we can't see but people are responding to moves other people are making. I cannot for the life of me understand why you would do this to yourself..."

Labour went through a series of leaders before finding the one who could take them to victory. Mr Trotter expects the same will happen to National.

"National is entering that terrible deadzone where all eyes are only on the leader - not on policy, not on the party, the deadzone that Labour lived in for nine long years."

Newshub.