Staff reporter and RNZ

Under-fire National MP Sam Uffindell has been stood down from the party's caucus, pending an investigation into further "very concerning accusations" surrounding his past behaviour.

In a statement late on Tuesday night, National Party leader Christopher Luxon said he had been made aware of new allegations about Uffindell's behaviour toward a female flatmate while Uffindell was at university in 2003.

The woman has told RNZ Uffindell was an aggressive bully who once pounded on her bedroom door, screaming obscenities, until she fled through her window.

Uffindell has denied any accusations he was involved in bullying or intimidatory behaviour while at university.

This morning National Party leader Chris Luxon told Newstalk ZB's Mike Hosking the situation was very concerning.

"You got a situation where a young woman, a flatmate has made serious allegations. It is a concerning situation for a father whose daughter is flatting, it's very real. They are serious allegations that need to be investigated. Sam is disputing the allegations."

Asked if Uffindell still had his backing, Luxon told TVNZ: "We'll find out in the next few weeks because really, what this investigation is about, is looking at both sides of that investigation."

Luxon also acknowledged that the investigation was needed to honour the "alleged victim" too.

The new allegations came a day after revelations that the new Tauranga MP, as a teenager, beat up a younger boy at boarding school.

"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 under way, Mr Uffindell will be stood down from caucus."

Former flatmate's accusations

Uffindell's former flatmate, who RNZ agreed not to name, lived with him and three other Otago University students for several months in Dunedin in 2003.

She told RNZ Uffindell engaged in a pattern of bullying during their second year at university, describing him as "verbally aggressive".

Uffindell would trash the house after "excessive" use of alcohol and drugs, she said.

"This was intimidation. This was bullying. I didn't feel safe," she said.

The woman said she eventually moved out of the flat after having to lock herself in her bedroom to avoid a drunken outburst one night.

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

"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."

The woman said it was not an isolated incident: "it was just the straw that broke the camel's back." Her father travelled to Dunedin the next day to help her move out, she said.

Speaking to RNZ, the woman's father corroborated his part in the story and said his daughter had been "seriously upset".

"The flat itself was completely trashed. There wasn't a stick of furniture left. There was no crockery left. There were no handles left on anything. It had all been broken."

He said he gave Uffindell and two of the other flatmates "a serious piece of [his] mind" at the time.

"It was clear... [Uffindell] had real issues, real problems... he was out of control."

The woman said she was traumatised by the event and did her best to avoid Uffindell from then on: "my stomach would absolutely flip and drop if I saw him".

Looking back, the woman said she should have spoken to someone or taken some sort of action, but she was too scared. Uffindell never apologised for his actions, she said.

She said people may try to excuse Uffindell's actions because of his age, but the pattern of behaviour revealed his character.

"Listening to his maiden speech in Parliament, he talks about lack of accountability and a sense of impunity - I think that's so hypocritical."

Uffindell's response

In a statement and while not addressing the specific allegations, Uffindell admitted engaging in a "student lifestyle" while at university.

"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 into the latest allegations would be conducted by Maria Dew QC and is expected to take two weeks.

"As the party only became aware of these allegations this evening, the details of the investigation will be finalised over the next few days, including the terms of reference." Wood said in a statement.

"In the interests of letting due process run its course, I will not be making additional comment on this issue while the investigation is carried out."

Uffindell - who won the Tauranga byelection in June - had apologised to the boy he assaulted in 1999 while at King's College.

In multiple interviews on Monday, he claimed the attack was the "stupidest" thing he'd ever done and still regretted the incident. On Tuesday he admitted to being a "bully" and a "thug" when he was younger.

Speaking to the Herald on Monday, Uffindell said he believed the assault on the then 13-year-old boy 23 years ago would become public during his running in the Tauranga byelection this year.

When it didn't, Uffindell chose not to tell the public until it was revealed by Stuff on Monday - a decision he still stands by, despite saying he had "taken ownership" of the incident and it had made him grow as a person.

He also revealed he may have tackled other students during the "raid" of the third form (Year 9) dorm that saw him expelled, in addition to punching one student in the arm and body several times.

The investigation into allegations against Uffindell will be conducted by Maria Dew QC and is expected to take two weeks. Photo / Supplied

Earlier on Tuesday, Luxon said he was standing by Uffindell after news broke of the assault, but insisted he should have been told of the incident earlier.

"He has my backing and he has my support but clearly he needs to build back trust with the voters of Tauranga," Luxon said.

Luxon confirmed that Uffindell had declared the incident to the National Party when he sought to be a candidate.

"He is not the same person that he was 22 years ago as a 16-year-old."

Luxon said he should have been informed earlier. The delegates should have been informed and the voters of Tauranga should have been informed earlier.

He said Uffindell's admission during selection had triggered deeper background checks and he believed that was how it was supposed to work.

Luxon said National's character checking extended to speaking to people who had known Uffindell since after the King's College incident.

"There was a deep exploration of this issue with Sam."

While the violence committed at the school was "totally unacceptable and abhorrent", Luxon said he had been assured that Uffindell did not have any other incidents in his past.