United Future leader Peter Dunne says he is was a victim of "extreme muck-raking" during the investigation into how a Government Communications Security Bureau report was leaked to media.
Mr Dunne resigned as a minister earlier this month after refusing to hand over emails to the inquiry into the leak of the Government Communications Security Bureau (GCSB) report to Fairfax reporter Andrea Vance.
Mr Dunne has denied leaking the report.
He told TV3's The Nation that continuing as a minister was not tenable in the circumstances.
"Could I have toughed it out? I don't know, I didn't really think that was appropriate."
The last couple of weeks had been tough on his family, friends and associates, Mr Dunne said.
"I think that this has been a most extreme form of muck-raking, and I think it's been hard on all concerned, and I just hope we can move forward from here and put those things behind us."
"I'm ... also a victim of my activities and actions, and do I feel regretful - in some senses yes.
"But look; I've fronted up, I took the call that it was not appropriate for me to carry on, and I'm now looking forward to the new horizons that lie ahead."
His wife Jennifer had been supportive, and the two had become much closer because of the situation, Mr Dunne said.
He did not know if the GCSB had spied on him.
"I suspect for a lot of New Zealanders the question that they will ask themselves in this whole debate is just how certain they can be of their freedom, how certain they can be that they aren't inadvertently caught up in something much wider.
"And I think that while these things always operate in the shadows to some extent, the challenge is to give the greatest level of confidence you can to people that their circumstances are being protected and their rights and freedoms are not being abused."