Undercover police unfairly used emotion-charged stories about their terminally ill parents to entrap minor players during a big cannabis operation, says a New Plymouth defence lawyer.

Police swooped on 35 gardening businesses across the country in April. The two-year Operation Lime resulted in 250 arrests and more than 700 charges, having busted more than 100 commercial cannabis growing operations.

One of those arrested was New Plymouth shop assistant Reuben Wade, 25, who had been unfairly taken in by the undercover female detective who visited Guru Gardener, his counsel Paul Keegan said yesterday.

Police transcripts of the conversation between the two reveal that the officer had told Wade her mother was terminally ill with cancer and asked for help to grow cannabis plants to help alleviate her pain.

"Police have set him up," Mr Keegan said. "It was a terrible thing to go into a shop and use a story like that. It is entrapment. It's effectively harassment by the police.

"They have entrapped him into having the knowledge that it will be used for cultivation. It's quite appalling."

It was not until nine months after the undercover operation that Wade was arrested and charged with two counts of supplying drug-related equipment following the sale to the undercover officer of a book on how to grow cannabis and some fertiliser.

Yet the book Wade sold could easily be bought elsewhere – as could the fertiliser, Mr Keegan said.

Results from a search of the Whitcoulls' website comes up with the same book Wade sold to the police officer along with 179 other marijuana-related titles.

"It really makes a mockery of the law. It is clear that some reform is needed," Mr Keegan said.

Last week in New Plymouth District Court, Wade pleaded guilty to the two indictable charges. He will be sentenced on August 16, when Mr Keegan said he would make strong comments in mitigation.

In his submission to Judge Blaikie, Mr Keegan said that his client's charges were very much a sideline to the major operation elsewhere in the country.

"This offending in relation to the New Plymouth store is largely unconnected with the wider operation involving more serious charges in other stores around the country."