New Zealand is not as honest and free of corruption as it likes to believe, according to a new report.

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This country along with Denmark were ranked equal first by Transparency International last year as the least corrupt places in which to do business.

Read the full report here.

But accounting firm Deloitte's latest bribery and corruption survey has found that about 20 percent of New Zealand companies surveyed had detected some form of corruption - about the same level as the previous survey two years ago.

"The perceptions differ from the reality. Corruption is real in New Zealand, it's happening and that's evidenced by the cases coming before the courts," said Deloitte forensic director Lorinda Kelly.

In February, Stephen Borlase and Murray Noone were each jailed for five years, and a third man was given 10 months' home detention, in a bribery case involving the awarding of contracts at Auckland Transport.

Ms Kelly said two thirds of companies feared their reputation would be shredded by corruption, but surprisingly many had done no risk assessment about their vulnerability, and more than half had no plan to take steps to bring in anti-corruption measures in the next five years.

She said the best defence was a company culture that made it clear that at all levels of a company the highest standards of ethical behaviour are expected.

"It's a matter of tone at the top that makes it clear that certain behaviours are not OK and that there is a way for people to speak out and make it known that things are happening that shouldn't happen."

She said the most common form of corruption was undeclared conflicts of interest, followed by gifts and trips, along with doing favours, and giving excessive commissions. The most common form of detection was tip-offs or whistle blowing.