Sam Uffindell's political future is in serious doubt as National's leader refuses to confirm the new MP will stay on if allegations about his behaviour at university are substantiated.

It comes amid a revelation Christopher Luxon's office knew of Uffindell's 1999 King's College bullying incident, but did not inform the party leader in a "regrettable" but "genuine" mistake.

Uffindell could not be contacted at his Paengaroa home. It was understood he was travelling from Wellington to Tauranga, driven by fellow MP Todd Muller who had been a mentor to the young politician.

Late on Tuesday, Luxon announced an investigation into allegations made by a female flatmate of Uffindell when the pair studied at Otago University in the early 2000s.

The flatmate said Uffindell had been an aggressive bully who once pounded on her bedroom door, screaming obscenities, until she fled through her window.

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 told RNZ.

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

In a statement, Uffindell said he enjoyed a student lifestyle while at university, which included "drinking" and "smoking marijuana".

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

He said he wouldn't comment further while the investigation was carried out.

Tauranga MP Sam Uffindell is facing fresh allegations from someone he lived with while studying at Otago University in the early 2000s. Photo / Mark Mitchell

Uffindell has been stood down from the party caucus while the two-week investigation, conducted by Maria Dew QC, takes place.

It comes after National's newest MP described his younger self as a "bully" and a "thug" after Stuff revealed Uffindell had punched a fellow King's College student several times during a late-night attack in 1999.

Uffindell, 16 at the time, was asked to leave the school the following day.

Luxon, who said dealing with the King's College incident was "immensely frustrating", would not confirm Uffindell's position in his caucus if the allegations were accurate.

"All I'm saying to you is [they are] very serious allegations, I want to have a dispassionate, independent investigation, there are two sides to this story, this allegation, and at the end of it, I'll take those findings and I'll make a decision."

Christopher Luxon was grilled over why his staff didn't tell him about Uffindell's King's College bullying incident when they were informed by Rotorua MP Todd McClay. Photo / Mark Mitchell

As an electorate MP, Uffindell would have to agree to resign from Parliament for another byelection to take place.

While National could eject him from its caucus, he would be able stay on as an independent MP unless National invoked the waka jumping legislation – which allows it to kick out an MP in such a circumstance.

National opposed that legislation, and did not use it when Jami-Lee Ross, the former Botany MP, was kicked out of caucus in 2018.

On Tuesday, Luxon said he was disappointed he hadn't been informed of Uffindell's high school bullying when it was disclosed to National's nine-member pre-selection committee ahead of choosing a candidate for this year's Tauranga byelection.

However, he revealed committee member and Uffindell campaign chairman Todd McClay had in fact told Luxon's staff of the incident after Uffindell's selection as National's candidate, but it wasn't passed on to the leader.

"That is regrettable and it's a mistake," Luxon said.

National MP for Rotorua Todd McClay (left) and leader Christopher Luxon. Photo / Mark Mitchell

The lack of information given to Luxon has seen one former high-profile MP Chris Finlayson say it was imperative leaders knew all they could about their MPs' background - both good and bad.

But Luxon defended McClay, saying he had done "nothing wrong".

McClay and the committee had come under fire because neither Luxon, party delegates nor the public were aware of Uffindell's bullying prior to his selection to contest the byelection and his subsequent victory.

Both Luxon and new National party president Sylvia Wood acknowledged questions needed to be asked of the process as a result.

"The selection process was run in accordance with the National Party rules, which require confidentiality," Wood said in a statement.

"However, it is now clear that process could be further improved, and we are looking at how best to achieve that."

Meanwhile, Finlayson said the selection process for MPs should be taken seriously.

"John Key used to say I can't help you until you tell me everything," Finlayson told Newstalk ZB's Mike Hosking this morning.

"The leader deserves to know everything; how can he help a rookie MP if he's being spoon fed information."

When asked about the gap between the party and its leader, Finlayson said it was a result of party working in a bubble.

"There needs to be a close nexus between the party out there and the party in parliament.

"It is totally foreign to me, you really need the party at large to work closely with party in parliament, the leader needs to know everything."