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Colin Craig claims ownership of poem allegedly written for former press secretary
He has threatened to take Slater to the Disputes Tribunal over the issue next year.
Part of the poem reads: "There is only one of me it's true, but I wish this were not the case, because I wish that I could have you."
Manhire, a professor of literature poet laureate from 1997 to 1999, said the work read "as if it were written by a 19-year-old male who was desperately in love with someone but didn't quite dare say it out loud".
But Mr Craig had a good ear, he said.
"Though you don't get a sense of it when you see him on the television, do you?"
Mr Craig could rhyme in a way that was not intrusive, he said.
"He's got a pretty good ear, it's not doggerel. In fact, if you look at the first line of the second stanza, 'if instead one man I was two' - If he'd made it 'if instead of one man I was two' it would be really clunky, so he's sacrificed a tiny bit of grammar for the music of the line."
The poem was a bit cliche, but not completely, Manhire said.
"There's a fine line between saying the thing that's true for most people and making it sound like a hallmark card or a bunch of old platitudes, and I think it's got a little more edge.
"He puts on a mask for the world, and then there's the true inner person who has all these powerful feelings, reminiscent of the line in TS Eliot's The Love Song of J. Alfred Prufrock 'prepare a face to meet the faces that you meet'," Manhire said.
"The idea that you would have a public face, which is the person that you present to the world, and another person who's the person who yearns away."
Despite Mr Craig's apparent knack with words, Manhire said if the poem was handed in by a student of poetry he might suggest they worked on it a bit more.
And if it had been submitted in application to Victoria University's exclusive creative writing course?
"He wouldn't walk straight into the class, but he wouldn't be rejected outright. He'd be put in the pile to be thought about quite seriously."
In an interview with author and journalist Steve Braunias ahead of last year's election, Mr Craig spoke of his soft spot for poetry.
"There was something else going on with him," Braunias wrote, "flair, inventiveness, the mind of an artist. At school, he wrote short stories and poetry."
In the interview, Mr Craig's brother Andrew recalled a poem he'd written about an atomic bomb, saying "it wasn't too bad".
Mr Craig also spoke of learning to play the guitar so he could write songs, and using creative writing as an outlet when he was a teen.