Gardai suspect crime gangs worked together to bring €30m 'black cocaine' shipment into Ireland

Sources said it was unlikely any one gang here would have taken on the risk linked to the delivery of such a large consignment of drugs.

And such concerns proved to be clever enough, given that investigators had been ­waiting for the shipment - that ­contained half a tonne of ­cocaine ­disguised to look and feel like charcoal - when it arrived in two containers in Rotterdam Port last month.

The containers were placed ­under surveillance but no one turned up to collect them.

The authorities in Holland then agreed to allow the shipment continue on to Ireland, this time under guard of the Irish Navy, as Irish customs and gardaí had been behind the operation to track the shipment.

South American drug cartels have been disguising cocaine as charcoal for a number of years, with numerous shipments transported like this.

The traffickers add charcoal and other chemicals, which transform the drug into a black ­substance that has no smell and does not react when subjected to the usual chemical tests.

The shipping containers that are believed to be filled with pure cocaine were escorted into Dublin Port last night by the Irish Navy.

The Dutch police had agreed to send the shipment to Ireland because the operation was ­initiated by gardaí from the ­National Drugs and Organised Crime Bureau.

The officers, who are supported by members of the Revenue Customs Service and Irish ­Naval Service, played a key role in the operation which had been coordinated through Europol and had also included work by the Dutch police.

The investigation involves a ­particular focus on a suspected ­attempt to traffic cocaine into ­Ireland from Columbia, using ­"intermodal" containers.

"In the course of the relevant investigation, the Garda National Drugs and Organised Crime Bureau has taken possession of particular containers, following their arrival in The Netherlands," a Garda spokesman has said.

"It is suspected a quantity of cocaine may be concealed there.

"However, the presence of cocaine within the containers cannot be confirmed until such time as the necessary examination and analysis is undertaken."