The largest covert drug operation ever seen in the Wellington region is now heading for a lengthy trial of almost three months.

More than 80 charges were laid after Operation Walnut, against eight defendants.

Up to 150 police officers raided properties throughout Wellington over two days in April this year.

At the time, police said they uncovered a grenade, more than $450,000, about 2kg of methamphetamine, and locked safes.

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Some of those arrested allegedly sold drugs to undercover police officers as far back as December last year.

Today in the High Court Justice David Collins told lawyers the trial had been set down for 11 weeks in July next year.

A large amount of police material and evidence is still being submitted to the court.

Police have previously said the four-month investigation focused on the supply and distribution of methamphetamine throughout Wellington, allegedly by members of Porirua Mongrel Mob.