Exemptions would apply to the family home and personal goods such as art and jewellery and vintage cars.
Tax would be applied after an asset is sold and on the gain in value between April 2021 and the sale price.
In a December 2017 briefing from Inland Revenue to Nash's office, officials said the lack of a comprehensive CGT "indirectly incentivises R&D as when a business ultimately decides to sell its idea, it is not subject to tax".
An IRD briefing five days later to Nash's office added: "A final point is that there is currently no capital gains tax, which is potentially advantageous to start-ups."
Both briefings were provided as background as the Government looked at bringing back a research and development tax credit, which was announced in Budget 2018 and rolls out tomorrow.
National Party leader Simon Bridges said the IRD advice showed that ignoring the working group's recommended CGT would help businesses.
"People who take risks with smart ideas and build something bigger than themselves shouldn't be discouraged.
"We need people who take risks and stretch themselves because the ones who succeed create more jobs."
A spokeswoman for Nash said the officials' advice was out of date and had been superceded by the Tax Working Group report.
Bridges also pointed to Treasury advice from August last year that said that a CGT could help the Government share in the benefits from additional R&D spending when those businesses or intellectual property were sold.
Bridges said it showed the Government wanted to use a CGT to "claw back some of the cost of the R&D tax credit."
But the spokeswoman for Nash said this was claim was "preposterous".
"The R&D tax credit was accounted for in Budget 2018, before the TWG even finalised its report."
The Government set aside about $1 billion over the next four years for a 15 per cent tax credit to any business spending a minimum of $50,000 on R&D.
R&D spending in New Zealand is currently 1.37 per cent of GDP each year. Boosting that to 2 per cent over 10 years is part of the Labour-NZ First coalition agreement.
As well as the R&D tax credit, a number of other Government measures come into force on April 1, including:
• Dropping ACC levies on average from 72 cents to 67 cents per $100 of liable earnings
• Adding new KiwiSaver contribution rates of 6 per cent and 10 per cent, and allowing those aged over 65 to sign up to KiwiSaver
• Lifting the minimum wage to from $16.50 to $17.70
• Increasing New Zealand Superannuation and Veterans Pension rates by 2.6 percent
• The right to 10 days' domestic violence leave and flexible working conditions
Prime Minister Jacinda Ardern has already sought to allay fears over how the Government's CGT decision might affect the small business and farming communities, saying they were "top of my mind when assessing options".
"I want them to know that I hear them," Ardern said a week after the Tax Working Group's report came out.
National has pledged to roll back any CGT that the Government might implement.
This week a Horizon Research poll showed 44 per cent of New Zealand adults supported introducing a capital gains tax, while 35 per cent opposed it.
A further 16 per cent were neutral on the new tax, while 6 per cent did not know.
