Finance Minister Grant Robertson is defending the decision to extend the fuel tax subsidy.

Chris Hipkins has announced the 25 cent fuel tax cuts, and half-price public transport will now run until the end of June.

Robertson said in December running it past the original March date wasn't sustainable, but that changed with Hipkins' succession.

He told Mike Hosking Hipkins wanting the cost of living at the top of the agenda was one of those factors.

Robertson says the policy has worked and therefore that was the policy they chose to extend to keep their cost of living focus front and centre.

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