National MP Sam Uffindell stood down pending investigation into allegations regarding female flatmate

National MP Sam Uffindell has been stood down from caucus after new allegations emerged about his past behaviour.

On Monday Stuff reported he had been asked to leave King's College as a 16-year-old after taking part in a group assault on a younger boy. Uffindell later apologised, and admitted he was a bully at school.

Now, a former flatmate has accused him of bullying and aggressive behaviour while at university.

In response, National Party leader Christopher Luxon said in a statement on Tuesday night that an investigation into the Tauranga MP would be carried out.

"This evening my office became aware of very concerning accusations made to RNZ about behaviour shown by Mr Uffindell toward a female flatmate in 2003 while at university," Luxon said.

"Mr Uffindell disputes the allegations and in the interests of natural justice, an independent investigation will now be undertaken to determine the facts. While this process is underway, Mr Uffindell will be stood down from caucus.

"However, as these allegations have only come to me in the last few hours, the finer details of the investigation, including the terms of reference, are yet to be confirmed and will be finalised over the next couple of days."

Uffindell's former university flatmate came forward after she lived with him in 2003. She told RNZ's Morning Report that he had a pattern of bullying, was "verbally aggressive", and would destroy the flat when highly intoxicated on drugs or alcohol.

She recalled one incident in particular was so bad she was forced to flee out her window to escape.

"He was smashing on my door and yelling obscenities and basically telling me to get out - 'hit the road, fatty'," she told RNZ.

"I ended up climbing out of my bedroom window and ran to a friend's house to stay the night. I feared for my safety. I was scared."

A statement from Uffindell said he rejects "any accusation that I engaged in behaviour that was intimidatory or bullying", but admitted drug use as a student.

"When I was a student at Otago I enjoyed a student lifestyle, which included drinking and, at times, smoking marijuana," he said.

"While in second year a number of flatmates fell out - and two of the flatmates left midway through the year.

"I reject any accusation that I engaged in behaviour that was intimidatory or bullying. This simply did not happen.

"While there is an investigation into these accusations I will not make further comment."

National Party president Sylvia Wood said the investigation will be conducted by Maria Dew QC and is expected to take two weeks.