Fifteen people accused of drug offences have pleaded not guilty at the end of a depositions hearing in Westport District Court.

Justices of the Peace Judith Johnston and Maria Hibbert ruled there was a case to answer, and committed the 15 to a pre-trial callover at the High Court in Christchurch on June 26.

The 15 deny involvement in what police allege was a commercial cannabis cultivation and supply ring.

A 14-month police investigation involved two undercover officers, phone taps, secret cameras in cannabis plots and hours of other surveillance.

The investigation, codenamed Marvel, culminated on December 8 when police descended on Buller to execute search warrants at multiple properties. Defendants were also charged in other parts of the country.

The depositions hearing was set down for two weeks, but finished early as the defence consented to 56 evidence hand-ups meaning evidence did not need to be read or cross-examined.

The three defence lawyers, Bruce Squire, Wayne Kerr and Doug Taffs, did not call any witnesses or present submissions. The defendants all pleaded through counsel, and had their bail conditions renewed.

Previously, an undercover officer gave evidence of her part in the operation. However, her lengthy brief of evidence, as well as subsequent cross-examination by Mr Squire, was suppressed at Mr Squire's request.

Detective Constable Alexandra York gave evidence that she interviewed Peter Cain after the December 8 raids. She said she put it to him that he was growing cannabis for Blair Colligan on land that ran adjacent to his own, owned by his father.

He denied he had been growing cannabis and said it was common for others to come on to land to grow drugs.

Operation Marvel defendants: * Shane Saunders, 38, of Cape Foulwind, faces 21 charges, including cultivating, conspiring to cultivate, offering to supply, and selling cannabis, conspiring to supply ecstasy and methamphetamine.

* Carl Grant, 39, Westport, 12 charges, including cultivating, conspiring to cultivate, and supplying cannabis, conspiring to supply ecstasy, possessing a firearm (while cultivating cannabis), conspiring to supply methamphetamine and ecstasy.

* Kylee Grant (formerly Duggan) 34, unemployed, Westport, a single charge of conspiring to sell cannabis.

* Bryan Anderson, 40, painter, Nelson, 12 charges, including conspiring to cultivate cannabis, selling ecstasy, selling cannabis, possession of a sawn-off shotgun, producing cannabis oil, and possession of equipment associated with the production of drugs.

* Peter Cain, 46, Waimangaroa, a single charge of conspiring to cultivate cannabis.

* Maria O'Brien, 35, Nelson, unemployed, five charges, including offering to supply cannabis oil, conspiring to sell cannabis, and selling cannabis.

* Natasha Peek, 30, cleaner, Westport, two charges, of conspiring to sell, and conspiring to cultivate cannabis.

* Robina Saunders, 60, Westport, three charges, two of selling, and one of possessing cannabis for sale.

* Joseph Tobin, 54, seaman, Porirua, three charges, including conspiring to supply ecstasy and methamphetamine.

* Paul Laidlaw, 46, carpenter, Glentunnel, three charges -- cultivating, conspiring to cultivate and conspiring to sell cannabis, all in Darfield. * Wayne Saunders, 40, manager, Christchurch, a single charge of conspiring to sell cannabis.

* Bevan Tetai, 30, operator, Cape Foulwind, charged with possessing cannabis for supply, selling, cultivating, and possession of cannabis resin for selling.

Three defendants had previously admitted there was a case to answer:-

* Alleged leader Blair Colligan, 28, Waimangaroa, who faces 12 charges including cultivating, conspiring to cultivate and supply cannabis, supplying a firearm, selling cannabis, conspiring to sell methamphetamine, conspiring to sell ecstasy, and possession of cannabis for sale;.

* Merehana Wihongi, 29, Waimangaroa, who faces two charges, of possession of cannabis for selling and possession of methamphetamine.

* Shaun Larking, 25, farm manager, of Westport, who faces charges of conspiring to cultivate, cultivating and selling cannabis.