(ANSA) - Rome, December 31 - A ban on the production and distribution of non-biodegradable plastic shopping bags comes into effect in Italy on January 1.

Shoppers will be offered paper or other biodegradable bags or else will dust off the kind of sturdy baskets used by their grandparents in what farmers' union Coldiretti on Thursday called "a revolution in the way we shop, just over 100 years since the invention of plastic".

However, stores will be allowed to use up their existing stocks of plastic bags, as long as they are offered free of charge, the industry and environment ministries said Thursday.

"In cooperation with the competent authorities, we will be watching to see that the switchover is carried out according to the rules," a joint statement from the ministries said.

"There is no going back", said Environment Minister Stefania Prestigiacomo, stressing that "producers have had enough time to prepare themselves for this change".

The government's plans to ban plastic bags, first drawn up in 2007, originally foresaw an end to their use starting from January 2010 before a one-year extension was granted.

This month a TV campaign has informed citizens about the ban and about environmentally friendly alternatives.

The environment minister is certain the ban will have a positive effect.

"Sustainability is made of little changes to our lifestyle that don't cost us anything and can save the planet." Italians have been using a total of 20 billion plastic shopping bags every year.

According to researchers, plastic bags remain in the environment for a minimum of 15 years to a maximum of 1,000 years, polluting the air, sea, rivers and forests.

A recent poll suggested that Italians are ready to do their bit, with 73% saying they would use alternatives to polluting plastic bags when out shopping.

These include biodegradable shopping bags and carrying bags made of natural fabric such as cotton, hemp and other materials.

Unionplast, an association that includes firms in the plastic production sector, criticised the ban, arguing that the European Union didn't have specific guidelines prohibiting plastic shopping bags.

According to the association, plastic bags are not a threat to the environment because they can be recycled.

Unionplast also pointed out that alternative, biodegradable shopping bags break more easily as they are not as strong as plastic, and also cost three times as much.

However, leading Italian environmental organisation Legambiente has praised the government's plans and echoed Minister Prestigiacomo's comments by reminding producers that the starting date for the ban was announced well in advance, giving them enough time to plan ahead.

Several countries including Britain, the US and China have planned plastic shopping bags in the last decade.