Act President John Thompson says he was left with the clear impression by former Act leader Don Brash that an approach by him about National MP Maurice Williamson joining Act had been made on behalf of Mr Williamson.
Act has rebuffed the bid and Mr Williamson is refusing to talk about it.
But Prime Minister John Key said today Mr Williamson assured him through a text exchange that he did not ask anyone to make an approach on his behalf.
"He made it really, really clear that he hasn't asked anybody - he hasn't made any approach and he hasn't asked anyone to advocate for him."
But Mr Thompson told the Herald that when he met Dr Brash in an Auckland central café the week before last, Dr Brash said something like:
"Maurice has indicated he would like someone to approach the Act Party on his behalf."
He was also left with the clear impression that the bid to join Act was a plan to "party-hop" now.
"No by-election was discussed," Mr Thompson said.
He and David Seymour, the Act leader and Epsom MP, opposed the idea, as did all other members of the board.
Mr Williamson was forced to resign as a minister in May last year when Herald investigations editor Jared Savage revealed Mr Williamson had contacted a high ranking police officer about domestic violence charges laid against a wealthy businessman to whom he was close.
It is highly unlikely Mr Williamson would be made a minister again.
Act blew the whistle on the approach yesterday in its weekly newsletter, Free Press.
Mr Seymour later said that taking on a new MP who was having problems with his party was the worst possible reason for getting a new MP.
Mr Seymour believed Dr Brash would not have made the approach to Act without Mr Williamson's authority.
"Don is many things but he generally acts very sincerely."
Dr Brash would not comment on the matter when asked whether his approach to Mr Thompson had been made with Mr Williamson's knowledge.
Mr Williamson has not returned calls.
If Mr Key had evidence that Mr Williamson had misled him, he could seek his suspension
from the caucus.
Mr Williamson was first elected to Pakuranga in 1987 and has always been considered close to Act, so much so that he considered joining Act for the 1996 election. That was the first election under MMP when Act was first elected to Parliament with Richard Prebble as leader.
Mr Williamson was suspended from the caucus after the 2002 election for being openly disloyal to then leader Bill English but was brought back into the fold when Dr Brash became leader in 2003.