It took a jury several days to decide whether the former MP Taito Phillip Field was well intentioned or corrupt when he accepted work favours from prospective immigrants. While the jury's verdict settles the question at law there will be those, not limited to his family, who continue to believe he is the victim of a cultural difference. This may not have been an argument advanced in his defence at the trial but it can be heard in public debate. A person of influence and importance in his community is expected to help people and accept their tokens of gratitude.

The argument falls down for Field somewhat because the people he was helping were not Polynesian and to refuse their reciprocal gestures should not have caused the same offence. But cultural conditioning tends to influence a person's dealings with everyone. In any case, the courtesy of accepting a reciprocal gift is known to all cultures. Field's crime was a failure to draw the line at an exchange of favours in public life.

It is hard enough for anyone in public office to draw the line between helping individuals who need it and favouring them. Most MPs spend much of their time helping constituents navigate public services and claim any entitlements their circumstances carry. They should do no more or less than they would do for any constituent in the same position. So long as no personal interest or prospect of reward enters the relationship, the MP remains on fairly safe ground.

As the first Pacific Islander to be elected to the New Zealand Parliament - as MP for Otara in 1993 - Field's constituency was wider than the Mangere electorate he took over from David Lange three years later. He would have been accustomed to helping people he knew well, or at least shared an identity with them. As an immigrant community they would have involved him often in immigration procedures and there probably is not a branch of government more prone to political influence than immigration permits.

One of the prime consequences of the Field case should be the removal of immigration decisions from a Beehive desk. It is wrong that individual cases can be taken to a minister - usually a junior minister and often not in the Cabinet - who has the power to overrule the decisions of officers who have applied the general rules and polices the Government has set.

No doubt the ultimate power is preserved for a minister in case bureaucratic consistency causes the occasional political embarrassment, such as the admission of an undesirable or the exclusion of someone who attracts public sympathy. But if exceptions need to be made at times, better they are made by an independent public panel than a politician in a quiet office accessible mainly to his parliamentary cohorts.

Sadly, there is no sign this will change now that the Field verdict is in. The Key Government seems as determined as any in the past to keep immigration close to its political chest. Immigration Minister Jonathan Coleman, ranked 19 in the Cabinet of 20, or his associate Kate Wilkinson, number 20, must ensure not only that their own dealings are beyond reproach but that any colleagues bringing cases to them have nothing personally to gain.

In explaining the work done for him, Field told the court, "I did not see it as a bribe ... friendships developed. It was friends helping friends". The jury found him guilty on 11 counts of bribery and 15 of wilful obstruction of justice for his testimony to an earlier inquiry.

Afterwards, the Crown prosecutor said, "This has been a really important case. Bribery and corruption strikes very much at the heart of who we are as a people." The verdict says we have a culture of public service that allows no favours in return, and that is a culture that rules all.