Labour leader Phil Goff has defended his decision not to stand down Darren Hughes after allegations were made against the MP, and has slammed the "trial by media" which ensued.

Police last week decided they would not be pressing charges against Hughes following allegations made by an 18-year-old student after a late night incident at the home of Annette King on March 2.

Mr Goff has been criticised for not standing down the Otaki MP down when the allegations arose. Instead Mr Hughes quit Parliament himself in April after the scandal became public.

Mr Goff did not believe Mr Hughes would still be in Parliament if he had been stood down by the Labour leader as soon as the accusation against him was made.

"If he had have been stood down at the outset that would have been against the presumption of innocence I think every New Zealander - whether you're a sports star, politician or radio journalist - are entitled to," he told Radio New Zealand.

He said the presumption of innocence is "fundamental" to the justice system.

"He was entitled to have his case investigated properly, as it was by the police, without the sort of allegations, wild allegations, that were made concerning him and the situation that in the end he felt made it impossible for him to continue in his role."

Mr Goff slammed the speculation made about the case through the media.

"The police are the body that are set up to investigate any complaint. We owe it both to the complainant and to the person complained about, simply to let them get on and do their job, and not to try their job for them through the media.

"A trial by media and an undermining of the presumption of innocence, I think are bad things."

The Labour leader said while police found Mr Hughes did not have a case to answer, his actions in March put him in a situation best avoided by public figures.

"It is always best when you are in the public eye not to allow yourself to get into circumstances that can be misunderstood or misjudged, and that clearly happened on this occasion," he said.

"I think it is the nature of life in the public sector, that when you are an office holder you're living in a goldfish bowl, everybody is intensely interested in what you do and how you do it. You are required to keep very high standards."

Mr Goff appeared keen for the MP to return to Parliament for Labour in the future.

"Darren Hughes was a very competent politician, he was very much admired and liked in his electorate, and won the respect of people across both sides of the House.

"What Darren does in the future is now for him to decide.

"I think the potential is there for him to come back, it won't be at this election, but that is a decision for him.

"Whatever the future holds, he will want to get on with his life, he will want to make decisions for his future, but at the moment he is simply thankful that the police have now said there is no case for him to answer."