EIGHT retailers are being investigated by the Revenue after they were discovered selling counterfeit cigarettes. The cigarettes display fake Irish tax stamps and came to light after a series of "test purchases".

A spokeswoman for the Revenue said the figure of eight investigations excluded separate probes into other smuggled cigarettes in markets and by street sellers.

The loss to the exchequer on a standard pack of cigarettes, retailing at €8.45, is €6.71. So far the largest cache of counterfeit cigarettes found in one shop has been 1,500.

Dermott Jewell, chief executive of the consumers' association, said it is "worrying that these bogus cigarettes have now penetrated the retail sector when it was always a predominantly black-market issue".

The retailers being investigated are in Cork, Waterford, Kilkenny, Louth and Longford. Irish brands such as John Player are now being targeted, as well as other brands such as Superkings. Smugglers are believed to be using the postal service to bring in the cigarettes.

The investigations come after customs officers two weeks ago seized more than eight million cigarettes in an anti-smuggling operation at Dublin Port with an estimated value of €3.5m.

The price of a pack of 20 cigarettes is considerably higher here than in other European countries, so Ireland is one of the cigarette smugglers' main targets.

The Revenue says it is too soon to determine how prevalent the black market here is until the investigations are completed.

"It is too early to say to what extent the market has been penetrated by the counterfeit product in question. The investigation is trying to trace the supply chain."