Two Dublin gangs who made fortunes out of cocaine dealing during the boom years last week followed Ireland's property developers into debt difficulties after major drugs seizures by gardai.

The Garda National Drug Unit seized two major hauls of cannabis with an estimated street value of up to €3m for which both had paid cash up front.

International police investigations have shown that even well-established Irish drugs gangs are no longer able to depend on credit when buying drugs.

All the drugs seized last week were paid for with cash, it is believed, to eastern European mafia based in the southern regions of Spain.

One gang from Crumlin, allied to the gangster Freddie Thompson who is currently on self-imposed exile in Spain, is understood to have paid €250,000 in advance for a shipment of cannabis resin which was eventually discovered by gardai at an industrial park near Dublin Airport.

A 28-year-old man who leads the gang along with his father was arrested near the scene but did not have direct contact with the drugs and has been released pending further investigations. He has been caught up in the gang feuding in south inner Dublin in recent years. An attempt was made to kill him or members of his family with a bomb earlier this year.

Another west Dublin gang is believed to have lost even more when the drug squad raided a warehouse in the west of the city.

According to senior garda sources the market for cocaine has more or less collapsed.

Many of the gangsters who amassed fortunes from cocaine dealing are believed to have squandered much of their wealth on extravagant living, particularly in the south of Spain, and are no longer credit worthy on international markets.

The biggest drugs gang in Dublin, led by figures formerly associated with the republican terror group, the Irish National Liberation Army, lost a major fortune last year when gardai and the Naval Service intercepted a huge haul of cocaine in the Atlantic.

The shortages of cash have driven gangs previously awash with drugs money to revert to armed robbery and extortion from other gangs to raise cash to buy drugs in Spain and Holland. The price of cannabis has rocketed in the past couple of years and with demand increasing the former cocaine gangs are moving back into the hash market. An ounce of cannabis which, in the mid-1990s wholesaled at €50, now sells on the street for around €300. The cannabis seized by gardai last week was of good quality and much stronger than that available in Ireland in the 1990s and before.

Garda involved in drugs investigations say young Irish people seem to have switched off cocaine. "The money's not there any more. We began seeing it from last year onwards. The clubs are half empty. They're not buying coke they way they used to," said one source.

The drug squad and the Organised Crime Unit, both based in Harcourt Square in Dublin, were behind the seizures last week along with gardai from Pearse Street Station who made follow-up arrests and seizures stemming from a major cocaine haul last year. Gardai from stations in west Dublin also assisted in the raids.

The heroin market remains on the rise. Gangs are now pedalling it throughout the country with the use of mobile gangs, one of the most active of which was led by Traveller, Thomas Joyce, 22, who was shot dead in Coolock in June.