Like the Denny Crane of New Zealand politics, Sir Roger Douglas sits in his 11th-floor office and flicks between brazen, brilliant and off-beat.

As with the Boston Legal character, Sir Roger's high points are largely behind him, but with the Budget coming up he's still showing plenty of game.

Sir Roger is hammering Finance Minister Bill English for being too soft before the National Government's first Budget is even out, having already given Michael Cullen a going-over for presiding over Labour's "sins" of the past nine years.

"I hammer everyone. That's what I'm here for," he said.

Sir Roger delivered his fair share of Budgets, and compared Mr English's with his first back in 1984.

The 71-year-old spoke of National's promised "line-by-line" reviews of Government spending in a been-there-done-that fashion and said it wouldn't deliver the savings they thought it would. He recalled divvying up Government departments with his Associate Finance Ministers Richard Prebble and David Caygill and each going line-by-line. "I did a third, Prebble did a third and Caygill did a third. You don't find that much."

He said line-by-line reviews were still useful to "get a feel" for department spending. "You ask them how many press officers they've got. They say 20. Then you ask them what the hell they have got 20 press officers for."

Mr English and his colleagues should instead be using a Treasury "hit-list" and knocking out big ticket spending items of over $20 million, such as Winston Peters' racing subsidies.

Sir Roger said even better savings would come by questioning whether departments such as the Ministry of Economic Development and Charities Commission were actually needed.

Sir Roger knows National will not go this far, although he predicted cuts would go deeper than many expected.

He said Mr English had been hit with a "hospital pass": Cullen's spending and the global financial crisis.

Sir Roger said like any hospital pass, Mr English simply had to take responsibility and "deal with it".

He said "all finance ministers have prime ministers to deal with" when preparing budgets. In his case, Sir Roger said David Lange "was too hard to take along - initially".

He sensed a different dynamic with Mr Key, "a Prime Minister who's popular, optimistic and has a pretty good feel for markets and own view".

However, despite the optimist-cautious divide between the two, he believed both would be eager to keep National's election promises.

It was the combination of keeping those promises and not making politically damaging decisions in other areas that meant the cuts would have to be deep in some places.

Sir Roger said that with the Prime Minister on board and the backing of associate ministers Steven Joyce and Simon Power, it would be much easier to win over the Cabinet.

Even so, horse-trading was a reality with the Cabinet process: "Having the support of some Ministers on the big issues can be a lot more important than cutting a couple of hundred thousand dollars out of their lines."

Sir Roger said he was enjoying his second stint in Parliament and was contemplating standing for Act again in 2011, when he would be 74.

His goal is still to "do my own thing" and has started writing another book, which will lay out subject areas that he will later expand into bigger personal projects.

And the topics on Sir Roger's personal hit list? So far there is education, ACC and local government - although he admits he'll have to run that one past leader Rodney Hide first.

1. Get the Treasury to prepare "hit list" for cuts.
2. Go after "big ticket" cuts - items of $20 million or more, such as horse-racing subsidies.
3. Question whole departments: "Do we need a Charities Commission?"
4. "Line-by-line" review should be last resort as it doesn't deliver real savings.
5. Watch for ministers trying to trick their way out of cuts by offering what they know you won't do.