Here’s what Wikipedia says about Bill English:
After completing his studies, he returned to Dipton to work as a farmer. In 1987, he returned to Wellington to work as a policy analyst in the New Zealand Treasury, returning to Dipton two years later.
In 1990 he stood as the National candidate in Wallace, the Southland electorate that encompassed Dipton, and won. He has been re-elected from this electorate, now known as Clutha-Southland, at every election since then.
Okay, so it seems that English lived in Wellington in 1987-89, returned to Dipton in 1989, presumably to re-engage with the local National Party organisation with view to gaining the Wallace candidate selection, which he won, and then to campaign for Parliament. He then returned to Wellington as an MP in 1990 following his election.
Then we have National Party MP Jackie Blue’s maiden speech:
I was extremely frustrated. It was John Harman who advised me to attend a Wellington Medical Women’s Conference in July 2001 to specifically lobby Annette King, the then Health Minister, who was opening the conference.
Madam Speaker I even bought a new red jacket to wear so I could be more appealing to Annette King.
I went to Wellington and, as fate would have it, also speaking at the conference was a Wellington general practitioner, Dr Mary English. At the conference dinner that night I spoke with Mary and she introduced me to her husband, Bill, who happened to be the Deputy Leader of the National Party. (my emphasis)
So the English family were well established as Wellington residents by 2001 at the latest, with both Bill and Mary working in Wellington by then.
So, how can Dipton be Sir Double Dipton’s “primary place of residence”? It appears there has been less than two years he has lived primarily there since 1987 (the time during 1989-90 when he moved back there to seek the National Party selection for Wallace and contest the 1990 election), and, on the word of a fellow National MP, he and his family appear to have resided solely in Wellington since at latest 2001.
UPDATE: Update: David Farrar is attempting to raise a defence for English that under section 72(6) of the Electoral Act, an MP does not become a Wellington resident just because they spend most of their time in Wellington.
The problem with that defence is that the provision is specifically for the purposes of the Electoral Act. Parliamentary accommodation expenses are not paid under the Electoral Act. They are paid from parliamentary appropriations pursuant to the Parliamentary Service Act and the Public Finance Act.
(6) The place where, for the purposes of this Act, a person resides shall not change by reason only of the fact that the person—
(a) is occasionally or temporarily absent from that place; or
(b) is absent from that place for any period because of his or her service or that of his or her spouse, civil union partner, or de facto partner as a member of Parliament; or
(c) is absent from that place for any period because of his or her occupation or employment or that of his or her spouse, civil union partner, or de facto partner; or
(d) is absent from that place for any period because he or she, or his or her spouse, civil union partner, or de facto partner, is a student,—
even if such absence involves occasional or regular residence at another place or other places. (my emphasis)