Gardai have smashed a suspected organised crime gang run by Poles living here.
This follows a series of raids in west Dublin and Meath yesterday when officers discovered eight cannabis growhouses and seized drugs with a street value of €1.6m along with €20,000 in cash.
The searches, which began at 6am, were carried out under Operation Nitrogen, which is controlled by the Garda National Drugs Unit.
The grow houses were found in Blanchardstown, Clonee, Mulhuddart, Porterstown and Navan. Detectives, backed up by gardai from the Dublin West division, seized 1,600 cannabis plants and seven kilos of herbal cannabis in the raids.
Last night the investigation spread overseas as gardai examined a link between the gang and an organised crime outfit based in the UK. There is no Irish criminal involvement.
Gardai believe the growhouses were producing a high quality product for distribution here and in the UK.
Five Polish men, aged in their 30s, were arrested and taken to Blanchardstown and Ballymun stations for questioning. They can be held without charge for up to seven days.
Detectives said the four were suspected of being active at varying levels of the criminal enterprise.
But they are also satisfied that information gleaned as a result of the operation has confirmed the identities of the main players in the gang.
They said last night that more arrests were expected as they expanded their inquiries.
Growhouse gangs have been forced to change their tactics because of the recent series of garda successes in seizing plants from industrial-sized warehouses.
They use smaller growhouses to ensure that one seizure does not capture their entire crop, and instead of hiring out warehouses they are converting rented houses and apartments into growhouses.
Growhouse plants usually produce about 40 grams of cannabis but those seized yesterday were estimated to produce up to 80 grams.
Each plant is worth around €800 and the price on the street for a 'deal' of herbal cannabis has jumped from €12 to a maximum of €25 in the past two years.
Gardai said the size of the cannabis market has increased substantially in the past couple of years as the customers of head shops switched over to herbal cannabis when the shops were shut down by new legislation.