National Party leader Simon Bridges says the capital gains tax is an "incredibly bad idea" which could damage New Zealand businesses.

The Tax Working Group has recommended a capital gains tax on investment property, shares, farming and other businesses at the taxpayer's highest income tax rate.

Exemptions would apply to the family home and personal goods such as art and jewellery and vintage cars.

Speaking with Kate Hawkesby, Bridges said this is something that Kiwis feel strongly about.

"The valuation that everyone will need so they can work out how much gain there has been."

"Take business this will potentially cost them, well I said $10,000, [but] I think in some cases it would be much more than that. That is a half a billion dollar cost across our economy that business often don't have. It is yet one more reason why this is a bad idea."

When asked about the Serious Fraud Office investigation, which was announced yesterday, Bridges said it won't get in the way of his campaign against the proposed CGT.

"I don't want to say too much about that because it's the SFO. I just want to say two things, firstly, this is for the National Party [and] you may say, well I'm the leader but...if you take me personally the SFO hasn't talked to me, there's no chance of any issues. I don't solicit, arrange or have anything to do with the logistics of donations, so there is nothing here."

Police yesterday said they had referred the handling of a political donation to the SFO, based on a complaint made by former National MP Jami-Lee Ross.

While Bridges said his hands are clean, he wouldn't confirm that he would resign "if an arrest occurred".

Instead, he said there won't be an arrest and any issues are for the National Party to deal with.

When asked whether he would use the waka-jumping law and ditch Jami-Lee Ross, the National Party leader said, "no".

"No one is interested in him...they are just not interested in him. I am going to talk today to several hundred people and I doubt they will raise him."

Bridges then turned his attention back to the capital gains tax, saying it is something that every Kiwi is exercised by.