In the perfect world, former Prime Minister Bill English would receive a dignified farewell from Parliament and the National caucus would unite behind a new leadership team.

But this is the real world of politics.

The relatively graceless response of Winston Peters to English's retirement news was an immediate reality check of the brutality of the process.

In contrast to generous comments about English by Ardern and James Shaw, Peters said he would leave the pleasant comments to others.

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And in the real world of politics, even if the National caucus manages to unite behind a new leadership team, it is not likely to last.

We've had a lot of practice of leadership changes in New Zealand and political parties are unforgiving beasts.

Labour has had six leaders in the past 20 years. National's next leader will be its sixth as well in the same period.

Disunity afflicted two of Labour's leaders (David Shearer and David Cunliffe) and three of National's (Jenny Shipley, Bill English the first time around, and Don Brash).

Every time it was the case of an Opposition party up against a popular Prime Minister.

If Ardern continues as she has, and if the economy shows no sign of deterioration, National will almost certainly drop in the polls.

Whoever the next leader is, Amy Adams, Simon Bridges, Paula Bennett or even Judith Collins, expectations may be unrealistically high.

They should be low compared with Bill English, who has been in a league of his own as a political performer in the National Party, and compared with the political phenomenon of Jacinda Ardern.

In the absence of a consensus candidate, disappointed candidates and supporters will inflate expectations, hasten failure and disunity.

The next leader of the National Party may not be the one that takes them into the 2020 election.

English has given the caucus two weeks' notice to choose a replacement.

That is time enough to sort out a consensus leader and deputy, although none has yet emerged. But that is no guarantee against later disunity.

Labour's selection of the consensus candidate of Phil Goff in 2008 merely delayed the inevitable emergence of disunity from disgruntled supporters of David Cunliffe which set the party back for years.

Sometimes it is better to just get on with a brutal blood bath.