What started off as a half compliment turned into rude insults and a sacking.

Police are investigating abusive emails sent by one of their prosecutors to a magazine columnist. Gisborne police prosecutor Claire Stewart called columnist Steve Braunias an "ugly f***er ", provoking him into an even more abusive response.

His Sunday contract was ended after he emailed Stewart back, saying: "Oh now I get it, you're a c***."

John Haigh, a Queen's Counsel who specialises in crime and employment law, said increasing numbers of workers were getting into trouble for inappropriate emails.

"Rule number one is, pause before you send any email which is likely to be damaging to you in terms of an employment relationship or offensive to an individual you are communicating with," he said.

Now Stewart, too, is under investigation for her use of her NZ Police email account.

Inspector Craig Tweedie, the national manager of police prosecutions, said: "Police are investigating the matter of the use of email by an employee.

"The employee will remain in their role until such time as the investigation has been completed. Police have strict rules around the use of police email and alleged breaches are treated seriously."

Stewart, who has worked as a prosecutor for the Gisborne police for nine years, told the Herald on Sunday she used her work computer because she did not have a computer at home.

"If I had a home computer I would have done it at home," she said.

Bizarrely, the abusive email exchange escalated from an emailed compliment - albeit a double-edged one. "You're not the most handsome of men, but what a beautiful mind and heart you have," Stewart wrote.

But when Braunias quoted her email as an example of why he hated his readers, Stewart took offence - and told him so in the strongest terms.

Sunday is a small insert magazine in the Sunday Star-Times.

After Stewart complained to the newspaper about Braunias' abusive language, editor David Kemeys apologised to her.

Braunias, who writes for both Metro and North and South, was told his services were no longer required as a contracted columnist on Sunday.

When asked for comment this week, Kemeys said he had none to make.

However, in a previous tit-for-tat on the issue in the NBR business newspaper, Kemeys said the matter was private, but "columnists come and columnists go."

Braunias retorted, "Editors come and editors go".

He told the Herald on Sunday yesterday, "I have no hard feelings towards Claire and I hope she will be all right.

"But every village has its idiot and the one here is Kemeys who made a stupid decision, which isn't one that Claire or the readers of the column would agree with."

He said he had sent Stewart flowers and an apology, but that had not saved his job.

It was "not out of character", he admitted, for him to use the C-word.

"You know, if I get something I judge to be offensive and abusive then I am not going to turn the other cheek," he said.

"I just read about a man in the Gisborne District Court - he got jailed this week for swearing at a judge. I should count myself lucky."

Claire Stewart said she had never asked that Braunias be sacked and regretted the whole exchange.

"This whole thing started by my wanting to pay him a compliment for his column, so I was gobsmacked by the whole thing, to be honest."

She acknowledged that, on email, meanings could sometimes be misconstrued. "But it's pretty hard to misconstrue what he called me."