"That was a disaster - they should never have put me with that woman," he grumbled to staff. "Whose idea was that? It's just ridiculous ..."
Asked what Duffy said, he replied: "Oh, everything! She's just a sort of bigoted woman that said she used to be Labour."
Most commentators saw it as the nail in the coffin for Brown, whose party was already sliding to defeat.
But don't expect any release of the Epsom teapot tapes to have a similar effect on John Key and National, says political marketing commentator Claire Robinson of Massey University.
For a start, she argues, look at how the Brown gaffe played out.
"All the British media pounced on that and said it was a train wreck of unbelievable proportions and this would sink Labour.
"Well, Labour didn't sink any further from that point ... and in fact in that electorate Labour's vote went up."
Even though hidden or forgotten microphones can show a huge gap between politicians' public statements and their private beliefs, Robinson thinks most voters accept this as normal human behaviour.
"Ordinary people, I think, recognise that politicians are allowed to say things in private that they may not necessarily say in public.
"All we want is leadership really. We don't need to know how they got to the point of making public statements."
Public reaction seems to depend on a number of factors, including how the recording took place - deliberately or accidentally in the Epsom case - and whether people believe the public importance of the revelations outweighs the way the information was gathered.
The closest parallel to the current case dates back to 1989, when an unseen tape recorder revealed former Labour Prime Minister Geoffrey Palmer getting a bollocking from his press secretary.
Former NZPA journalist Joanne Black later confessed in the Listener that she accidentally left her machine behind after a particularly longwinded and impenetrable Palmer press conference at a Commonwealth Heads of Government meeting in Kuala Lumpur.
When she played back the tape she heard Palmer's press secretary Karren Beanland tearing strips off him for talking too quickly and not giving direct answers. Palmer apologised and said he didn't think he could do it any other way. Beanland said he could if he tried but he wasn't trying hard enough. Palmer apologised profusely again.
Black didn't publish the conversation but did play it to other journalists in the Press Gallery. Word quickly spread to the National Party and Ruth Richardson gleefully recited the conversation in Parliament.
Black said she immediately apologised to Palmer and tried to imagine the tape would have no effect on him politically. She later realised she was kidding herself when she read Helen Clark's comment in her biography; "It was things like this that just made him terminal."
In 2005 former Labour MP John Tamihere seemed to forget all about the microphone in an extended rant to Investigate magazine editor Ian Wishart about his own party.
Tamihere, who later said he believed the conversation was off the record, infamously referred to women in top positions as "frontbums" and rubbished Labour's left wing as politically correct and run by gays and unionists.
To some extent his views were no surprise - he had always been on the blokey right of Labour. But his graphic, unflattering descriptions of senior Cabinet ministers (Steve Maharey was "very smarmy, very clever, but no substance") was an insight into the party's internal wrangling and hugely embarrassing for the Government.
Will the teapot tape have a similar effect? Robinson says the hottest topics appear to be speculation that Act leader Don Brash will miss out on a seat in Parliament and a claim by Key that NZ First's support is dying out with its elderly voting base.
Both issues have been well covered in the past and aren't controversial in themselves, she says. The potentially embarrassing point for National is that they don't fit the tightly scripted release of information of an election campaign.
She thinks the contents of the tape could be intriguing for some voters because they represent a secret kept hidden from the rest of us.
"But for most people - not for the media - that's pretty short-lived, as they move on to other things."
Psychologist Sara Chatwin agrees, saying most people's curiosity to know what's on the tape probably comes second to the feeling that we would not want our private conversations recorded either.
"I mean, how many times have you gone out for a beer with a mate and talked about somebody behind their back? Probably a lot.
"We would all have that moment where we would go 'Eek! I do hope that some of what I said wasn't heard' because as humans we do have a tendency to critique.
"The big issue here too is that all of this stuff is taken out of context. Was it said in a joking, light-hearted way? And how do we know that someone hasn't edited it so that it looks awful and really wasn't that bad."
Robinson argues that journalists, who resent being manipulated by politicians and felt especially set up by the tea party stunt, have a different attitude to knowing what's on the tape than the general public.
"I think if you walk into any public bar ... you'll find there are other things they are interested in.
"This is a beltway thing about the politicians' relationship with the news media rather than something which is going to be of great significance for voters."
She predicts it could have a short-term impact but National will bounce back by election day.
The biggest losers in her view are the minor parties, who traditionally get some exposure in the second-to-last week of an MMP campaign, as voters consider their coalition options.
Close up and caught out
1. United States President Barack Obama and French President Nicolas Sarkozy were this month overheard discussing Israeli Prime Minister Benjamin Netanyahu.
"I cannot stand him. He's a liar," said Sarkozy.
"You're fed up with him? I have to deal with him every day," Obama replied.
2. Former US President George W. Bush greeted British Prime Minister Tony Blair with "Yo, Blair!" at a G8 summit in 2006. Their lunch conversation, captured by a TV technician's hidden microphone, later moved on to birthday presents.
"Thanks for the sweater," said Bush. "Awfully thoughtful of you. I know you picked it out yourself."
Blair jokingly replied: "Oh, absolutely, in fact I knitted it myself."
3. A lipreader revealed Britain's Conservative Prime Minister David Cameron and his Liberal deputy Nick Clegg were discussing the National Health Service as they sat waiting for Obama during his London visit in May.
"Most people want to change it," said Cameron.
"Well," Clegg replied, "what you mean is you want to change it!"
