Wealthy businessman Roshan Nauhria willing to financially back Gaurav Sharma

Newshub can reveal rebel MP Gaurav Sharma has the financial backing of one of New Zealand's richest Indian businessmen - Roshan Nauhria.

The Prime Minister is still yet to set a date for the Hamilton West byelection - triggered by Sharma's resignation - but is already attempting to paint Labour as the "underdog".

Jacinda Ardern ventured to Hamilton West to campaign alongside Sharma ahead of the 2020 election. Both will be trotting back for a byelection - but this time on opposing teams.

"My hope is that it wouldn't happen at all," she said on Wednesday.

Hopes are free, democracy is not. By-elections cost about $1.2 million to run, funded by Kiwis.

"It's a waste of taxpayers' money," Ardern said. 

"I completely acknowledge the cost of the by-election and it is unfortunate that this is what it has come to."

It has come to this as Sharma was convinced the PM was going to kick him out of Parliament using the waka-jumping legislation spurred on by the Labour Party recommending that Sharma be expelled from the party.

"I pre-empted it. I want to make sure the people of Hamilton West have a voice in Parliament, whoever they choose," said Sharma.

But Ardern said she has no idea where he got that idea from.

By-elections are expensive for the taxpayer and a raid on political parties' war chests ahead of election year. 

"The Labour Party always puts money away for a rainy day," said Labour's Megan Woods.

"We are going to be ready to go. We are going to have a great candidate. We are going to have a great campaign," said National leader Christopher Luxon. 

"It's going to be very hard for me to run this by-election. I don't have the machinery. I don't have a similar amount of funds," said Sharma.

But Newshub can reveal Sharma has cash if he wants it.

Nauhria, a wealthy Indian businessman and former leader of the failed People's Party, has told Newshub he will both bankroll Sharma himself and seek donations from others to help out too.

"I will support him financially, 100 percent. Wholeheartedly… [it] doesn't matter the money, whatever he needs."

Sharma said he's received lots of offers of support.

Labour's trying to label itself the longshot before anyone has even picked a candidate.

"In recent times we have been the underdog in that seat. I do think it would be a very robust and tough by-election," said Ardern.

Sharma said Labour isn't the underdog as "they have huge machinery behind them".

They're managing expectations in case Labour gets trounced in the Tron.