Election 2020: Judith Collins 'disgusted' after Jacinda Ardern's dig over her past with the SFO

Opposition leader Judith Collins says she's disgusted at the Prime Minister's response to National's plan to double the Serious Fraud Office's budget.

National announced on Tuesday it would double the Serious Fraud Office's budget if elected, to investigate more cases of fraud, bribery and corruption.

"The SFO takes very few prosecutions, not because there isn't fraud, bribery and corruption in New Zealand, but because the office doesn't have the resources to do its job properly," National leader Collins said in a speech.

She pledged to double the SFO's budget from $12.7 million a year, to $25m, and said it would be renamed to the "Serious Fraud and Anti-corruption Agency", which, Collins said, made clearer the focus wasn't only on white-collar crimes involving private companies.

But Labour leader Jacinda Ardern took a jab at the stance, referring to Collins' resignation from a ministerial post in 2014 due to an engagement with the SFO.

"Interesting to hear now ... there's obviously a little history there with the Opposition leader and the SFO," she said.

"As a previous minister, her engagement with the SFO led to her job loss."

Judith Collins told Heather du Plessis-Allan it was "a very low blow" and said an inquiry had cleared her of any inappropriate action.

"I was disgusted with that response from her and clearly she's wrong," she told du Plessis-Allan.

"I just thought 'goodness sake, where's the kindness gone now?' I thought she wanted a clean campaign and that was pretty dirty."

National Party leader Judith Collins told Heather du Plessis-Allan Ardern's comments were "a very low blow". Photo / Greg Bowker

Collins, once the Minister responsible for the SFO, resigned that and other ministerial portfolios in the lead-up to the 2014 election, after an email emerged that appeared to link her to a blog campaign to undermine former SFO boss Adam Feeley.

Then Prime Minister John Key initiated an inquiry, which found that while Collins had provided information about Feeley to WhaleOil blogger Cameron Slater, "there was nothing improper about the provision of this information".

Collins was later reinstated to Key's Cabinet.

She told du Plessis-Allan Ardern was probably nervous about tonight's MediaWorks debate.

"Gosh, the veil is definitely slipping, isn't it?"