Don Brash's second very public coup for the leadership of a political party has thrust him from the footnotes of political history back into the action.

And if he can revive the Act Party at the election in seven months, he might return to Parliament a different politician from the one that shuffled out of the House in 2006 as a former National Party leader.

Brash has always been blessed - or cursed - with huge self-belief but he is bolder, older and, with no time to lose, likely more demanding in a confidence and supply agreement than the present party.

If, as Act leader, he doubled Act's support from its present five MPs to 10, the party could expect a darned sight more than a 2025 Taskforce, Regulatory Standards Bill, a commitment to reconsider competition against ACC workplace cover and a couple of ministerial posts.

And if Act held the balance of power by being the only support party on offer, the policy demands would be even higher.

That is the sort of scenario in which the leader of a small party can demand to be finance minister.

It is the sort of scenario that is easy to draw.

While Labour leader Phil Goff has been quick to suggest that National is thrilled about the Brash takeover, the person second-most thrilled, after Brash himself, has to be Goff.

With the prospect of a further right agenda, spending cuts and privatisation, and the possibility of Don Brash as finance minister (let's see if John Key rules that out), Brash is offering Goff a lifeline as well as the Act Party a way to drag votes from the centre-right.

John Key has been presented with a very complicated challenge. He has to forge a new relationship with a political enigma not known for his political finesse while leading a party that has been riven by infighting for most of its life.

Brash hinted last night he does not want Hide to continue as a minister, and what he says must count. Ministerial appointments to parties are not a private matter. Both leaders need to agree - that is, Brash and Key.

The safest place for Act may be on the cross-benches between now and the November 26 election.

But where Brash will really be tested is in his promotion for Epsom of former Auckland City mayor John Banks, a former National minister who will join Act if he gets the nod.

Banks would win easily - actually, anybody endorsed in Epsom by Brash and Key would win easily.

But not everyone in Act sees two old Nats for the price of one as the bargain Brash paints it to be.

The first couple of months will be testing for all.