The clean slate law was primarily designed for those who have committed lesser crimes but a High Court judge has concealed a the history of a paedophile in a landmark court case.

A former teacher convicted of repeated sexual offending against an 11-year-old boy has been granted a clean slate so he can work in aged care, despite objections by those in the industry and another judge.

It is the first case of its kind to reach New Zealand's High Court, with those convicted of sexual offences ordinarily exempt from the law designed for people who have committed lesser crimes.

The Kiwi man, who cannot be named, applied to conceal his historical offending under the Criminal Records (Clean Slate) Act 2004 so he could embark on a new career in aged care.

But his request was initially declined by Judge Lawrence Hinton in the District Court, who said it was for aged care providers - not the courts - to make employment decisions.

"I believe the chosen employers here must be able to choose for themselves ... I have concluded that an awareness of [the man's] previous convictions is appropriate in the public interest," he said.

However, on appeal to the High Court, the man was granted his clean slate.

"This appears to be the first case of its type to reach the High Court," Justice Mathew Downs, who heard the appeal, said in his judgment released to the Herald this week.

The man's offending occurred when he befriended an 11-year-old at a children's camp before indecently assaulting the boy during the 1980s.

A decade later the offender confessed to his flatmate, who told her mum.

When she learnt the man was a teacher in the late 1990s she informed police.

The man was charged and promptly pleaded guilty before being given a suspended sentence of imprisonment and ordered to a term of community work instead.

Police overseas had also investigated the man and searched his home after a complaint.

The police report referred to him possessing "a large quantity of information pertaining to paedophilia".

The man's conviction resulted in a lifetime ban from teaching children, but he later lectured adults in New Zealand and overseas.

A spokesperson for the Teaching Council of Aotearoa New Zealand, which is responsible for the register of teachers, said if a person's conviction was a specified offence under the Vulnerable Children Act it would still be disclosed in a police vet even if it was clean slated.

The clean slate law allows a person to be automatically eligible if they have never been sentenced to a custodial sentence, been crime-free for the past seven years, and have never been convicted of a list of "specified offences".

Those offences are a series of sexual crimes, largely against the young or vulnerable.

But there is an exemption, which Justice Downs said was "at the heart of this case".

A person who is guilty of one of the "specified offences" can ask a judge to exercise discretion and disregard their conviction, but only if they had not served prison time.

A judge, under the law, also has to balance "the interests of individuals in concealing their criminal records against the wider public interest in the safety of the community".

A psychiatrist, police expert and psychologist, and another doctor - whose name was withheld because they knew the offender personally - all considered the man's case.

They said he posed a low-risk of reoffending, while work in aged care would be a low-risk environment.

However, affidavits from four aged care employers - each of whom had read the medical reports - said they would not employ the man, irrespective of the expert opinion.

His lawyer, Dr Roderick Mulgan, argued if his client was not granted a clean slate "word would be all over the city" once he applied to work in aged care.

Justice Downs said the prospect of work in the industry was "largely illusory" and he was left with a "stark" choice.

"Either [the man's] record is concealed or, in all likelihood, he will not be able to work in the aged care industry," his decision reads.

The well educated man was "fortunate" to be given a "lenient" sentence for his offending, the judge said, but appeared suitable for aged care work, despite already enjoying "meaningful employment".

But the safety of the community involved residents of rest homes and visiting friends and family, but "most obviously, grandchildren", Justice Downs said.

"The case is on the cusp," he added.

"Contact with children in that sector is likely to be limited, and even more likely to be in the company of others. Offence opportunity is therefore low. This aspect, remorse, and the consensus of expert opinion ... tip the balance in his favour."

The man said he "deeply regrets" his offending and had spent the past 30 years repenting.

The man, through his lawyer, did not wish to comment on the case.

New Zealand Aged Care Association (NZACA) chief executive Simon Wallace said because of the vulnerability of residents, aged care providers closely check a person's criminal past.

"Ultimately, protecting the safety of residents and employees, and the families that visit our facilities, is of paramount importance to the sector," he told the Herald.

"Our members follow very robust recruitment processes, which in certain instances will certainly include looking very closely at previous criminal convictions and sexual offending would be a very serious concern."

As for the clean slate legislation, Wallace said it was not for the NZACA to argue its merits.

"The legislation exists for a reason and it is up to the judicial system to make those calls where non-disclosure is deemed appropriate," he added.

There are, however, exceptions to the clean slate rule, Justice Downs explained in his judgment.

"For example, if someone has applied to act in a role predominantly involving the care and protection of a child or young person, he or she must disclose any criminal record."

Those applying for a firearms licence must also disclose, wanting to be in a position which involves the national security of New Zealand, a judge, justice of the peace, community magistrate, police employee, prison officer, probation officer, or security officer.

A person who enjoys the benefit of a clean slate also loses it if they are convicted of any offence.

The latest Ministry of Justice statistics show more than 160,000 people have had their criminal record - which includes more than 830,000 convictions - hidden since the law came into force in 2004.

The clean slate scheme is automatically applied by the ministry when an application is made for a copy of a person's criminal record.

There is no central register or list of people meeting the criteria at any one time.