Controversial TV news boss Bill Ralston says it is almost time for him to leave the job which has seen a public end to some of television's best-known faces.

As head of TVNZ's news and current affairs department, he has revealed the massive changes he was employed to achieve are now almost complete.

His time at the helm has seen newsreader Richard Long canned, Paul Holmes depart for Prime, and the end of an 18-year career for anchor Judy Bailey.

Behind the scenes, it has also seen the sacking of news chief Melanie Jones.

According to Ralston, it was all part of his grand plan, set out in his 6000-word job application to chief executive Ian Fraser in 2003.

He told the Herald on Sunday on Friday that he would stay as long as it took for the changes to take effect - but didn't expect that to be for much longer.

"I'll probably get it all sorted and when I'm happy with it, I'll wander off and go back to doing what I was doing, which was enjoying myself.

"A couple more years would be fine, as far as I'm concerned; a year or so. That's the end of the challenge."

TVNZ has suffered a huge backlash over some of the changes. However, both Ralston and Fraser say the changes were necessary and will ensure TVNZ's success for the next 20 years.

Fraser described the past week, and the end of Bailey as the One News sole anchor, as "tough". "It was a tough call, but it was a call that had to be made."

He said the changes followed on from the strategy Ralston arrived at TVNZ with.

"I don't think there has been any deviation from that. The problem is he couldn't do it all at once. Change is hard for any organism to withstand if it's never-ending."

According to Fraser, Ralston was keen to see more reporter-driven news on air.

Fraser praised Bailey as a "bloody good broadcaster" but said One News needed to be refreshed.

"I accept there will be people for whom right now I am the lowest form of life. That comes with the territory." He has signalled a return to the two-person anchor format, and spoken highly of Agenda frontman Simon Dallow and Tonight host Kate Hawkesby.

Fraser acknowledged his job was on the line if the changes failed: "I begin to take responsibility if we fail. But we're not going to fail."

He described Ralston as "extraordinarily effective" and said TVNZ had not deviated from his strategy. "One of the things that happened almost immediately was we went to a single anchor-format. Richard Long left. That was a very important part of Bill's plan at that stage. It was clearly right for the time.

"We moved directly back into a position of pre-eminence."

In Holmes' case, it was a matter of measuring performance against viewer feedback, planning succession and being unwilling to meet his demands.

Ralston said his strategy had proved a good blueprint.

"I knew from the start what we were getting into and it would be enormously unpopular with some traditional viewers, but I also knew you had to go through that process of reinvigoration."

It was not possible to make the changes in one move because it would "destabilise" the successes achieved, he said.

" ... I came in to do these changes. That's what I was told to do, that's what I offered to do and that's what I've done. I never at any stage thought it would be easy ... and I don't care. I have a hide like a rhino anyway."

Ralston said his aim was to take TVNZ news from the late 80s "and bring it well into this century again and create a base from which we can have another 15 to 20 years of relative stability".

He said his job was almost done. "We are witnessing now the last of the big changes."