ACT's Mt Albert by-election candidate wore the brunt of his opponents' frustration with the proposed Auckland Super City when he was smeared with cake at a debate today.

John Boscawen attended the hour-long Unitec debate alongside fellow candidates - Labour's David Shearer, National's Melissa Lee and Green Party co-leader Russel Norman.

As Mr Boscawen spoke of the virtues of changes to Auckland's local governance, People Before Profit by-election candidate and Super City opponent Malcolm France surged forward from the crowd and smeared his head with a slice of chocolate lamington cake, In Unison student magazine editor Stacey Knott said.

"It was pretty sudden.

"And then this guy just ran up and smeared cake on his (Boscawen's) head and then retreated back to the crowd and then, I think, security took him out."

Ms Lee, whose own campaign has been mired by a series of blunders, helped Mr Boscawen clean off the cake and the debate continued.

"There was a bit of shock but he kept carrying on as usual. John Boscawen didn't really do anything he just continued his sentence," Miss Knott told NZPA.

Mr Boscawen said at first he thought it was "wet squeegee" on his head.

Not wanting to lose his allotted speaking time he continued to talk, he said.

"Yes, when I was speaking I had a person come and squash a lamington on top of my head."

The rest of the debate went well, Mr Boscawen told NZPA.

Ms Lee also drew attention today over an email, allegedly from her, speculating a gun may be helpful in dealing with the media.

The email was in response to questions from the student magazine about which accessory she would prefer - a gun, a fur coat, a big diamond ring or a grill.

"I think a big diamond ring would be the most useful accessory during the rest of the by-election to knock some sense into the media (although a gun is tempting...)," Ms Lee replied.

The email was unapproved and sent by a volunteer who was trying to do her a favour, she said today.

Prime Minister John Key said he had not seen the email.

"But, it certainly hasn't been my approach (to use a gun)'s bits of paper as a general rule."

Mr Key said he would campaign with Ms Lee and hoped she won the seat, despite her admission last week the she hoped to come second.

"We go into every election and by-election with the intention of winning.

"We also go in with a realistic attitude."