"This lot" was a reference to the Labour Party and potential coalition partners, a scenario Mr Banks says is best avoided by Act returning to Parliament to support National.
On current polling, this could happen only if he wins Epsom. It could also be avoided if National wins an outright majority, or goes into coalition with other parties, such as current coalition partner the Maori Party.
Mr Banks has struggled in recent polls, with one reported but unconfirmed poll suggesting his support would take a hit if voters felt National would win outright.
A Herald on Sunday poll this month had Mr Banks trailing Mr Goldsmith by 14 percentage points, though 42 per cent of those polled said they were undecided.
The debate saw Mr Goldsmith and Mr Banks echo each other in extolling the virtues of Prime Minister John Key.
When asked if he wanted voters to vote for him, Mr Goldsmith said: "No, I want the party vote. That's the main thing.
"It's no secret that in the last two elections, the majority decided it's worthwhile sending an Act person in to support a National Government."
Meanwhile, Labour candidate David Parker, MP, struggled to be heard over the parroting comments from the right, resorting to a list of Act scandals and comparing a vote for Mr Banks to a vote for cerebral flatulence.
"What [Epsom voters] don't want is a repeat of the perkbuster [Rodney Hide], David Garrett [resignation], the brain farts from Don Brash and a return to the Chicago School of Economics theory which has led the world to the debt we have.
"A vote for John Banks will bring back the Act circus and I don't think that's good for New Zealand."
He said his standing in Epsom had nothing to do with his party leadership aspirations.
Mr Banks tried to characterise Labour as the party to borrow, tax, spend and hope, but Mr Parker countered that by saying Auckland City Council more than trebled its debt in the last three years of Mr Banks' mayoralty.