NZ First leader Winston Peters may have issued an apology for 2008 and a battle cry for 2011 - but one of the party's former members of Parliament, Ron Mark, has turned his back on the party.

Ron Mark was NZ First's highest-profile MP after Mr Peters himself - and yesterday said that after 12 years with the party, he was no longer active and would not rule out returning to politics with another party.

The Newsroom website revealed yesterday that Mr Peters has written to party members and apologising for "mistakes" made in the election campaign.

When asked if Mr Peters' apology was warranted, Mr Mark paused for a lengthy period before answering:

"I think it's always important to acknowledge mistakes you have made.

"To me it's irrelevant right now. I'm out."

He said he was formally still a member of NZ First, because he had taken up a multi-year subscription and was unsure when it expired.

"But I'm not active. I've made no commitments to anyone on anything. I'm taking time out and enjoying doing the work I've been doing as a political commentator and speaking quite independently ... I'm doing what suits Ron Mark these days."

In the letter to party members Mr Peters said the party had reflected on "what went wrong" and it was now time to "prepare NZ First for the battle of 2011."

The letter begins with the apology for his handling of the campaign and ends by asking them to renew their subscription to the party.