"Enjoy!" Prime Minister John Key said as he drifted into his caucus meeting a few hours before delivering his self-described step-change for New Zealand. In Parliament later Labour MPs were indeed enjoying.

"Ha! Step back, more like," they shouted at the word step-change and "rubbish" when he said he would not embrace a policy of increasing GST unless it benefited New Zealand's economy and left most New Zealanders better off.

When he spoke of Australia's mining wealth and added "we too have great resources" the Labour MPs found one in Parnell.

"Yeah, the Prime Minister's house. Dig that up!"

Even right-wing blogger David Farrar was suddenly a font of wisdom and worthy of great respect after Labour discovered he had described the so-called step-change "b-grade".

Despite it all, Mr Key was still enjoying himself when he wound up his own speech, gesturing at Labour leader Phil Goff and saying while he had just set out a step-change the only policy Mr Goff had come up with was to cap the wages of 16 public service bosses.

He stayed chirpy through much of Mr Goff's response, playing on his BlackBerry as Mr Goff dismissed Key's speech as a "step-back" and wondered how those on the minimum wage would now afford the box of Weetbix their recent 25 cents an hour increase would have bought them.

He especially enjoyed it when Mr Goff criticised GST as a regressive tax and his National side loudly reminded Mr Goff he was part of the same Labour Government that had increased it the first time round.

But by the end of Mr Goff's speech, Mr Key was not enjoying. Instead he was fiddling with something on his desk uncomfortably as Mr Goff recalled a certain street called McGehan Close.

Mr Key had done Mr Goff the favour not only of raising the possibility of a GST increase - political manna for an Opposition in need of target practice - but also of raising the "underclass" again.

It was the "underclass" word which in 2007 led him to the "dead-end street" of McGehan Close in Owairaka where he met Aroha - the young girl he then took to Waitangi with the nation's media watching over his good deed.

Unfortunately for Mr Key, the Herald on Sunday had just last week gone back to McGehan Close to see Aroha's mother, Joan Nathan, who had delivered a right royal ear-clipping to John Key.

How Mr Goff relished that yesterday. "What do they say in McGehan Close now?" he asked and then answered himself: "Joan Nathan says she has been let down by the Prime Minister and her daughter Aroha now wants nothing to do with him. She says she and her family are worse off since National won the election. She says she's pretty "anti-John Key at the moment."

Mr Key kept his head down, gave a yawn and resumed fiddling.

For Mr Goff, it was even enough to make up for those National MPs shouting "Let's hear from Shane Jones" throughout his own speech.