The cultivation of cannabis plants in so-called grow houses has become a multi-million euro industry in Ireland, according to a member of the Garda National Drugs Unit.

Addressing the annual National Prosecutors’ Conference in Dublin Castle, Detective Sergeant Brian Roberts said that growers had become increasingly sophisticated.

He said they were now using advanced irrigation and heating systems which, in some cases, could produce cannabis with a street value up to €5m.

Also at the event the Director of Public Prosecutions called for the speeding up of the criminal justice system.

Claire Loftus said that effective pre-trial procedures are needed to save valuable court time, jurors' time and legal costs.

She said that the absence of such procedures severely affected the administration of justice in a timely way and noted that trials in the Central Criminal Court have average lead-in times of at least a year.

Ms Loftus said the vast majority of defendants ultimately plead guilty and that new procedures would dispose of issues that need not be left to the trial.

She said that a system was needed in which both sides and not just the prosecution were required to focus on the real issues in a case at an earlier stage.

This would save valuable court time and legal costs.