The Government says it's tweaking the Clean Car Discount scheme because it's working as intended.

It's announced it will have to lower the threshold for higher emitting vehicles and increase the fees on them and also change rebates for zero emissions imports.

When asked how many times this will happen, Transport Minister Michael Wood told Mike Hosking they always knew they'd have to review it every one to two years.

He says as more people buy clean vehicles, they will keep increasing the ambition of the scheme to clean up the fleet.

LISTEN ABOVE