Prime Minister Bill English has noticed one curious side effect of becoming Prime Minister: his old-fashioned chivalry is falling flat.

He says that since he became Prime Minister when he stands back to let a woman go through a door first, they will not go.

"I stand back and they stand back, because they don't think they should go ahead of me."

The exception, of course, is his deputy Paula Bennett.

"Give her half a chance and she's straight through the door in front of you."

This was sparked by a conversation about the perils of making any comment at all about a women's appearance.

Bennett is sitting next to him as the pair go through a series of media interview designed to showcase the English-Bennett team compared to the Key-English team.

By coincidence rather than design it is also now a comparison to the Little- Ardern team.

The interviews were arranged well before the turbulence in the deputy leadership as Annette King handed over to Jacinda Ardern.

But the timing ensures not all the attention is on the team on the other side.

Bennett has gone up against both King and Ardern in her time as a minister. Ardern was at the other end of Bennett's "zip it, sweetie" remark in Parliament.

A few hours earlier, Bennett had appeared with King on morning television and said if she too could serve her time with the "strength and dignity" of King, she would consider her career well spent.

Asked now if they had been "out-freshed" by the other side, Bennett laughs and English says "no."

"They're going to really miss Annette. They're a fractious bunch and they need someone like Annette to hold them together."

For the past eight years it has been English and former Prime Minister John Key doing these interviews trading sledges and compliments - and sometimes sledges disguised as compliments.

There is still a bit of that. When they are asked to keep answers "short and snappy," English says to Bennett: "She clearly doesn't know you very well."

English might have taken John Key's job and title, but he's not going to take the job description he himself once gave to Key in 2012 of "bouncing from cloud to cloud."

English can't spend as much time "grinding" away on the policy nitty gritty now that he is Prime Minister, but it is pretty obvious Bennett is now in charge of the bouncing bit.

It is she who knows what Lorde's new single is called - English has no idea.

Bennett was handpicked to go with English because of their different backgrounds and personalities - Bennett is more outgoing, from Auckland and urban rather than rural. It is a similar match up to that of Little and Ardern.

She has also picked up a rather more critical aspect of Key's role: as the barometer of "middle New Zealand."

According to English, it was Key who would sense when something would be a bit too much for New Zealanders and start to apply brakes.

"I find Paula actually, from my point of view, has a lot of the same sort of instincts. I listen pretty carefully to her instincts about it."

There are are actually three in this political marriage. The other is Finance Minister Steven Joyce.

For the first time in 15 years, the deputy leader is not also the Finance Minister - before the English-Key pairing there was Helen Clark and Michael Cullen.

The relationship between Joyce and English is even more critical than that between English and Bennett and Joyce spends just as much time in English's office as Bennett - especially with the Budget two months away.

Then there is the kitchen cabinet which meets regularly to chew things over: English, Bennett, Gerry Brownlee, Steven Joyce, Amy Adams, Simon Bridges and Jonathan Coleman.

English doesn't believe in change for change's sake. "It's a good system. It works."

In the small talk before the interview started, English and Bennett were asked to sit closer together for the camera.

"If I had bad breath you'd tell me, wouldn't you?" English asks her.

English and Bennett already knew each other well. He recalls his first memories of her as "a bit rambunctious. But that doesn't mean you shouldn't listen."

Since then they have worked closely together on the welfare reforms and social investment approach, a plan to identify and put money and resources into at-risk families early on to try to prevent flow-on problems.

English says despite their very different backgrounds there is an overlap in values especially in social policy. He is "a bit drier" economically and Bennett says she is "a bit more liberal."

Given English's Catholic views, that would not be hard.

Bennett describes it as a good working relationship.

English clearly knows her tricks. He will not reveal what his karaoke song would be on the grounds that she would then force him to sing it in future.

Despite further probing, he refuses to budge. "I've learnt. I know her. You don't give an inch."

Asked later if she managed to get his favourite karaoke song out of him, Bennett said she had not even tried. "He can be quite stubborn."

- NZ Herald