Rodney Hide’s declaration of allegiance to the man who had just cut his political throat was, I suppose, only marginally less bizarre than Don Brash’s compulsion to lead something, anything. One suspects that, if he had been thwarted in his drive to lead a political party, he would have announced his intention to found a new country, so that he could lead that instead.

Yet the extraordinary spectacle of the Don and Rodney show has a wider significance than the question of which of two egocentrics should lead a minor party on the margins of politics. Ever since the Labour Party was taken over in the mid-1980s by extreme “free-market” ideologues, New Zealand politics has struggled to recover some sense of what political labels really mean.

It is in everyone’s interests – and is certainly an essential element of a healthy political system – that politicians should take up positions that are consistent with their true beliefs and policies. The Labour Party has at last re-established a recognisably left-of-centre stance, which the voters – whether they support it or not – can identify and understand.

Don Brash’s migration to the leadership of the Act party is similarly helpful. It means that he is at last positioned where he should have been all along, and can now openly make common cause with his old mentor, Roger Douglas.

It also provides confirmation, if we needed it, that his brief leadership of the National party was an aberration – the product of a “hollow men’s” conspiracy, not just against the voters in general but against the National party itself.

It was, presumably, his success (albeit short-lived) in hi-jacking the National party – backed as it was by wealthy but largely undeclared co-conspirators – that explains his assumption that he could repeat the trick with Act. We should all be grateful that at least we all now know where we – and he – now stand.

Most of us will have been open-mouthed but relatively detached observers of recent events. For the National party, however, there may be real consequences of the change in Act’s leadership.

On the one hand, if Don Brash is right in arguing that his leadership will provide a lifeline for an Act party that was otherwise in a terminal condition, John Key will have good reason to welcome the change. The deal whereby an Act success in holding on to Epsom provides National with five or six additional support MPs will clearly be advantageous in the event of a close election result this year.

On the other hand, a close link in the voters’ minds between John Key and Don Brash may not be helpful to National’s chances with voters beyond the boundaries of Epsom. John Key’s cautious reaction to the prospect of Ministerial office for Brash, and his rejection of any possibility that the new Act leader might take an economic policy portfolio, show that he is all too aware of the possible risks to National of a higher-profile Act leader – particularly when that leader is Don Brash.

The risk is all the greater when the voters know much more now about Don Brash’s true politics than they did. Many voters will have concluded by now that we all had a lucky escape when Brash – in his National guise – was narrowly defeated in the 2005 general election. They will not welcome the prospect of a Brash re-entry to front-line politics through an Act back door.

That is especially true at a time when New Zealand voters are being asked to re-evaluate their MMP voting system (interestingly, at the same time as British voters will also vote on a possible proportional representation system).

Proportional representation inevitably throws up the issue of what role could and should be played in parliament and in government by small, perhaps extreme, parties on the fringes of politics. The fear of those who support first-past-the-post is that PR will allow extremists to exercise an undue influence over the government of the day.

The good sense of the New Zealand electorate has, however, done much to lay those fears to rest. MMP has largely delivered the more representative parliament that was promised, with better representation of women and minorities, and has ushered in a style of government that operates more by negotiation than by diktat.

And this has been achieved without sacrificing the central virtue of a first-past-the–post system – the voters’ ability to throw one lot out and replace it with another. The New Zealand electorate still chooses between a right-of-centre and a left-of-centre government, with a continuing assurance that small, extreme parties will not be allowed to exercise a disproportionate influence.

A major party that allowed that assurance to be called into question could pay a heavy price. John Key cannot let it be thought that a vote for National is a leg-up for Don Brash. The back-stabbing intrigues of minor politicians should not be allowed to mean the intrusion of extreme policies into our mainstream politics.