Environment minister Dick Roche has said he has been made aware that more and more retailers are ignoring the 15 cent levy, and he intends to stamp it out.

"From representations I have received there would appear to be some anecdotal evidence of slippage in application of the levy, " Roche said this weekend.

Inspections are to be carried out on shops and an enforcement network of local authority officers has been established.

"It is evident that the plastic bag levy continues to have a positive effect on our environment. I am anxious that it should continue to do so and in this context will keep all aspects of the levy, including the level of the tax, under review, " the minister said.

While the levy is supposed to act as a deterrent against using plastic bags, it appears that its effect has weakened over the four years of its operation.

The number of bags used by Irish people has increased from 70 million in 2002 to 113 million last year.

Similarly, revenue collected from the levy has soared from 7.1m in 2002 to 17.5m last year. The levy has raised over 55m since its introduction.

But with plastic bag litter beginning to re-emerge across the country, Progressive Democrats senator John Dardis has proposed raising the levy on plastic bags to 30 cent.

"I don't want to see plastic bag use creeping back in, " said Roche. The law permits me to increase the levy and I am disposed to doing that. I can only go to 19 cent under the existing law and I will do that. If necessary I will go to the Oireachtas and look for support to go higher."

Revenue from the plastic bag levy and the levy on landfill is paid into a ring-fenced environment fund. The fund is used to support waste management, recycling and other environmental projects.