Act must win Epsom if it fails to cross the 5 per cent threshold. It has been polling at about 1 to 2 per cent. Its campaign focused solely on retaining Epsom, but became enveloped in the teapot tape and speculation over what Mr Banks said to Prime Minister John Key during their conversation.
This cast doubt on the loyalty of Mr Banks to Dr Brash, who has dismissed the tape as a distraction and repeatedly said he has full confidence in Mr Banks.
Dr Brash has not helped matters by declining to rule out the possibility of leaving mid-term. He has said he intends to stay as leader for the full term, however.
Last night he dismissed the latest poll.
"My impression is that we are ahead in Epsom. The mood of the electorate has changed remarkably in the last few days as people wake up to the fact that Paul Goldsmith will go to Parliament anyway.
"There have been an enormous number of total diversions and a lack of understanding on the part of the electorate of how serious a shape the economy is in. People just haven't picked up on it."
Mr Banks said Act's polling had him and Mr Goldsmith neck and neck, with 17 per cent still undecided.
"A vote for Paul Goldsmith is not a vote for me. A vote that's not for me is a vote for Phil Goff, Winston Peters, Hone Harawira and the Greens."
He said he totally supported Dr Brash's leadership.
A National Party source said the Epsom race was too close to call.
EPSOM
National Business Review Epsom Poll:
46 per cent Paul Goldsmith, National
37 per cent John Banks, Act
12 per cent David Parker, Labour
3.3 per cent David Hay, Green