"You've got to really drive the public service to be able to think in such a holistic way, and to be totally focused on the difference you make in people's lives - to break cycles of violence and dependency - as opposed to just getting absorbed in the process of just spending money."
READ MORE:
• National Party leader Todd Muller has minor surgery
• National leader Todd Muller says Coalition Government is dysfunctional
• Todd Muller's new hire Matthew Hooton may cause disquiet among National MPs
• National leader Todd Muller says confusion reigns in Govt over alert-level 1
He said the public thought of National as the party of, among other things, building roads, which was important.
"But there's also significant social deficit, and I signal that that will be a priority."
Muller has given National MP Amy Adams, who was part of English's social investment team, a high place in his shadow Cabinet.
Social investment sought to use information and technology to improve social services, focusing on early investment to achieve longer term results and help people to be more independent.
National's previous leader Simon Bridges criticised the Government for shelving social investment.
Asked what Muller would bring on social investment that was different to former leader Simon Bridges, he said: "Part of it is the priority that you give it. Part of it is the values that you bring as an individual and your lived experience, which helps inform your thinking and your approach as a leader."
He said his speech tomorrow was not about new policy, but about who he is.
"People want to understand where you've come from, what your values are, your life experience and core political beliefs - what Prime Minister do you plan to be?
"That's what I lay out in fair detail."
Muller has had minor surgery this week to remove pre-cancerous moles. He said he could have fronted to media on issues of the week, but with bandages around his head, he left it to deputy leader Nikki Kaye.
Today's speech will be at the rugby club where he used to play as a lock, and next door to the club where he used to play tennis; he prefers Roger Federer to Rafael Nadal.
His wife Michelle, their three children, his brothers and the wider community will all be there.
"It's where my family have lived for 45 years, across the road from the church where we got married, the little convent school where I was the only Pākehā boy in the school.
"It is absolutely my tūrangawaewae, and people get to see that."
Muller was hardly a household name when he successfully rolled Bridges as party leader three weeks ago, but he says public recognition has since improved.
"I've been out and about and it's quite remarkable. I think it helps to be tall and bald, maybe. Certainly the level of recognition has been quite extraordinary."