Labour leader Phil Goff has announced that his MP Darren Hughes has been stood down from his portfolios while a police investigation into him is completed.

Mr Goff said Mr Hughes would remain in Parliament but he now expected the police inquiry to take longer than initially expected.

Mr Hughes' jobs as education spokesman and senior whip will go to David Shearer and Steve Chadwick respectively.

Mr Goff has also admitted he was wrong to call for Prime Minister John Key to sack Richard Worth soon after a police complaint was made against him.

Mr Worth resigned soon afterward and no charges were laid.

Mr Goff said he had now learned some things about the complexity of such situations.

"I'm going to be the first to admit I was wrong in the judgment I made at that time. People are entitled to be regarded as innocent until they are proven guilty. I believe I got it wrong, in hindsight, yes."

He said he did not believe his leadership was now under threat.

Although he had not yet held a full caucus meeting since the news broke, he said he had spoken to several of his colleagues.

Mr Goff said he stood by his original decision not to stand Mr Hughes down as soon as he was told of the complaint against him two weeks ago.

However, now that it was a "public controversy", it was impossible for Mr Hughes to do his job.

He said Mr Hughes had agreed with his decision to stand him down, and said he would do what was appropriate in the interests of the Labour Party.

Mr Goff said he believed Mr Hughes had "integrity."

However, he would wait for the outcome of the police complaint before making any further decisions about Mr Hughes' career.

He would not comment on whether he believed it showed good judgment for Mr Hughes to take home an 18-year-old, saying he would wait to see the facts before making a judgement.

Inside accused MPs' fateful night

Inside the packed Establishment bar in Wellington, Labour chief whip Darren Hughes was having a jovial time with some Victoria University students who had spent much of the night together.

It was 2am on March 2 and in the following hours, an incident allegedly took place in Mr Hughes' Hataitai home that triggered a complaint to police from an 18-year-old student.

It is understood the complaint - which Labour leader Phil Goff has been aware of for two weeks - is of a sexual nature. Mr Hughes, at 32 one of Labour's most promising MPs, has denied any wrongdoing.

Earlier that evening, from 6.30pm, Mr Hughes, a talented debater, had taken part in the Victoria University Great Debate at the Hunter Lounge in Kelburn, leading the negative team in the moot, "That there should be a universal liquor allowance for students".

Other debaters included National's Tauranga MP, Simon Bridges.

"It's part of the Victoria University Orientation Week, so there was a good crowd, people in good spirits," said Seb Templeton, president of the Victoria University Debating Society.

"Afterwards, people wandered into town in various groups. It was O-week, so everyone heads to town every night, especially the first-year crowd."

Mr Hughes, Mr Bridges and about a dozen students went to the Matterhorn bar and restaurant in Cuba St.

"We all had a bit of food, something to drink, and I left about midnight," Mr Bridges said. "I certainly didn't see anything inappropriate happen."

Mr Bridges said whatever occurred, if anything, must have happened long after he had left because police had not contacted him. He found out about the allegations only yesterday.

Mr Templeton said he later met the group again, including Mr Hughes, at The Establishment in Courtenay Place.

"There was nothing unusual going on. When I left [Mr Hughes] was just having a chat to people around him, being a good guy. He wasn't particularly drunk ... He seemed fine. Most people were in a jolly mood."

Later, the complainant went with Mr Hughes to the home of Labour deputy leader Annette King, where the MP boards. Police have visited the house and taken some items away.

They have not commented on reports that the complainant left the home early that morning and ran into a police car, when he made allegations against Mr Hughes.

Two days later, students began to receive calls from the police. Mr Templeton said he was interviewed within a week.

"I wasn't told of any of the allegations. I just gave them a rundown of what happened that night, including what drinks I had at which bars.

"They asked where the complainant was in relation to me when we were in the same place, but they didn't ask me about Darren at all, and at the time I had no idea Darren was involved."

Yesterday morning, police confirmed detectives were investigating a complaint against an MP.

"Inquiries into the matter are continuing but police are not seeking any assistance from the public at this stage," the Wellington district field crime manager, Detective Inspector Mike Johnson, said in a statement.

It is understood the complainant has no formal political connections but has an interest in politics.

Mr Templeton said the complainant was just getting on with life.

"He seems fine. I haven't talked to him about it. I don't think many people have. We're just waiting to see what happens. I can honestly say he hasn't told any of us what the allegations are."

A student, who did not want to be named, said the complainant was keeping up "his usual, confident personality" and had not discussed the incident at all, except with police.

A duty manager at The Establishment, Dushka More, said yesterday that police had not been in contact, and she did not know anything about media reports of officers wanting to look at video footage from the bar.

The Matterhorn also said police had not spoken to staff.