UK grocery retailer Sainsbury's will roll out their "eco-friendly" milk bags and jugs across their milk range, after a successful trial of 2% fat milk bags, which sold at double the expected rate.

Sainsbury's said that milk is one of their biggest selling lines. Shoppers are now buying 120,000 semi-skimmed milk bags per week - 10% of two-pint (.94 litre) semi-skimmed units sold. Sainsbury's said they expect this figure to double following the expansion, and that the change could bring an end to the "130 year reign of the milk bottle."

"This is the biggest change to occur to the nation's shopping habits for at least a decade," siad Sainsbury's senior dairy buyer Emma Metcalf King. "The familiar clink of the glass milk bottle could finally become a thing of the past."

To meet customer demand for milk bags, Sainsbury's and its supplier, Dairy Crest, have invested over £2.2million in a new processing plant at its site in Gloucestershire.

Full-fat 'Whole' milk bags were launched yesterday, while skimmed and 1% fat milk bags will launch in June 2011.

Polyethylene milk bags use 75% less packaging that standard plastic bottles, and cost less to the consumer and the manufacturer. They are used in conjunction with a JUGIT milk jug, which pierces the bag and creates a no-leak seal.

Sainsbury's began selling milk bags in all of its supermarkets in February 2010 to help meet its target to reduce packaging by a third by 2015. Sainsbury's said that customers switching to bags could save up to 1,400,000 kg of packaging every year.

The Sainsbury's success story is a contrast to the lackluster response to a similar product by rival supermarket Waitrose, who discontinued their milk bags in April due to poor consumer demand.

The popularity of the Sainsbury's product, compared to the Waitrose offering, may be attributable to a strong promotional campaign and storeperson training, and to a giveaway of 500,000 jugs to customers in April.

"Before launch, we gave free jugs to our store colleagues to make sure they understood how to use them. As a result, our colleagues have proven to be the best ambassadors for the product, as they are able to explain it to customers using their own personal experience," said Metcalf King.

Milk sold in bags is already a regular choice for 60% of consumers in Canada, Poland, South Africa and China.