Conservative powerbroker Nick Minchin has berated the head of Channel Seven Adelaide for publicly backing a candidate contesting the Liberal Party senate seat vacated by Mary Jo Fisher.

Tony Davison, the General Manager of Channel Seven Adelaide, wrote a letter of endorsement earlier this month for preselection frontrunner and long-time friend Anne Ruston. His endorsement was also included in a brochure sent to Liberal Party members ahead of tomorrow’s vote.

“I’m personally surprised that the general manager of Channel Seven would seek to inject himself into the middle of an internal Liberal party preselection contest,” Minchin told Crikey this morning. “I’d have though it’s rather odd and of dubious judgement for the head of a media organisation, which prides itself on political impartiality, to get involved in this.”

In the letter obtained by Crikey, Davison praises Ruston, who is backed by Christopher Pyne’s moderate faction (and who runs a small business selling roses), for her business acumen and communications smarts:

“Anne possesses excellent communication skills and I have no doubt these skills would prove an asset to the Party on the campaign trail, in the Parliament, as well as in day to day interactions with the community and the media.

“Please accept my personal endorsement of Anne. As a close business acquaintance and friend over many years I have no doubt she has the skills, energy and commitment to be an extremely effective senator for South Australia.”

Minchin is backing Ruston rival Kate Raggatt, who worked in his office for a decade. The former SA senator and Howard government minister says Davison’s letter is poorly timed given growing calls for tougher media regulation.

“The media are rightly concerned about the federal government’s proposals to regulate the media and are arguing that that’s not the place of government,” he said. “By the same token, the media need to not be seen to be directly interfering in the activities of political parties. To get so directly involved, to tell delegates how to vote, is very odd.”

Channel Seven spokesman Simon Francis says Davison’s letter is not an appropriate use of “company stationery”. His statement read:

“Seven is committed to political independence and that includes not supporting candidates. Whilst Tony’s letter makes it clear it was a personal endorsement for a replacement vacancy for an existing senate seat and not an elected situation, Seven confirms it was not an appropriate use of company stationery. Tony also wishes to make clear that it was not an endorsement for a political party but a personal reference for an individual running for preselection. He is not a member of any political party and has friends on both sides of politics.”

Francis says the letter would have been appropriate had it not been written under the company’s letterhead.

Bev Barber, who stepped down from her position as state director of the Liberal Party to contest the preselection, declined to comment when contacted by Crikey. The Liberal Party state council will tomorrow decide whether Ruston, Barber, Raggatt, Campbelltown councillor Marijka Ryan or farmer Gary Burgess will replace Fisher, who announced her retirement last month after being reported to police for shoplifting for a second time.

Greg Mayfield, editor of the Fairfax Port Pirie Recorder newspaper, was forced to withdraw from the contest last month after an internal Liberal Party review found his candidature was not in the best interests of the party.