UPDATED 4.39PM: The ACT Party is accusing National MP Maurice Williamson of trying to ditch his party for theirs.

ACT Leader David Seymour says the move was made through Don Brash, who suggested Williamson should join ACT's caucus, before the board rejected it.

But Mr Seymour says they don't need someone who's caused mischief in another party.

He added they want to give people positive reasons to vote for them, rather than getting involved with political game-playing.

Williamson was forced to resigned as minister in May last year when the New Zealand Herald revealed Williamson had contacted a high ranking police officer about domestic charges against a wealthy businessman with close ties to him.

Dr Brash, a former ACT and National Party leader, is declining to be interviewed about the matter saying he doesn't want to comment on the allegation.

Williamson's phone line remains unanswered.

Prime Minister John Key said Williamson has denied having any conversations with ACT, nor is he interested in leaving the National Party.

"Yeah, yeah, no, I believe him," he said. "Look if he wanted to go to the ACT Party he's had lots of opportunities over the years and he's never chosen to want to do that. He's very happy being the National member for Pakuranga and that's how he wants to stay."