Tweaking the Reserve Bank Act in a bid to increase employment will not work, according to former Reserve Bank governor Don Brash.

Labour Finance spokesman Grant Robertson wants to expand the bank's focus in order to achieve maximum employment.

But former ACT and National Party leader Dr Brash told Rachel Smalley this morning Robertson's thinking was outdated.

"Grant Robertson reflects back to a time when people thought you could actually affect employment in an ongoing way by monetary policy - we now know that's nonsense," he said.

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