Christine Rankin has resigned from the Conservative Party following former leader Colin Craig's admission of inappropriate conduct.

Mrs Rankin, the party's former deputy leader and chief executive, confirmed to the Herald she had quit the party this morning.

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Mrs Rankin quit as Conservative CEO after the September election, but remained a board member.

Colin Craig has admitted that some of his interactions with former press secretary Rachael MacGregor were "inappropriate", but rejects accusations of sexual harassment.

Earlier today, she said she was "very disappointed" in Mr Craig.

"I gave my brand to Colin Craig ... I feel very let down," she told Radio NZ.

Mrs Rankin said there was no future for the party if Mr Craig remained on board.

She had lost confidence in Mr Craig "a while ago" and challenged him after hearing about his conduct three weeks ago.

Mrs Rankin was also disappointed that the board had not acted more quickly in dealing with Mr Craig.

She had been tipped for the top job after Mr Craig's resignation on Friday, but said she had absolutely no interest in the role.

The former Ministry of Social Development head and Labour Party member joined Conservatives in 2012.

She had not wanted to return to politics but said Mr Craig had "begged" her to get involved and she believed in his vision for the country.

Conservative Party leader stands down as leader so party can review the position.

In 2014, she was ranked second on the party list and ran in the Epsom electorate, placing fourth.

Chairman Brian Dobbs said he had received Mrs Rankin's resignation letter.

"We thank Christine for her years of service on the board and as a CEO she has conducted herself admirably," he said.

Mr Dobbs said he was disappointed in Mrs Rankin's decision because he felt she had much more to contribute to the party.

Like her, he was frustrated that the board could not act more quickly in dealing with the allegations surrounding Mr Craig.

"But we must adhere to the process. It's unfair to all parties concerns if we don't."

Mr Dobbs confirmed that he had received a motion to cancel Mr Craig's membership at a board meeting on Saturday.

He said Mr Craig would struggle to make a comeback after admitting inappropriate interactions with his former press secretary Rachael MacGregor.

"Given the press conference ... and Colin's personal revelation of the situation, it's very difficult for any politician to come back from a situation like this."

But he said that once the board had considered all of the allegations against the former leader, he deserved to have a second chance.