Sainsbury's has hailed rocketing sales for milk sold in plastic bags after rival Waitrose decided to stop stocking the format due to high levels of waste.

Sainsbury's introduced the two-pint bags for semi-skimmed milk in 2008 and now sells around 110,000 bags a week, accounting one in every 10 two-pint containers of semi-skimmed milk sold.

The bags are designed to be used in conjunction with the Jug-it plastic jug made by RPC. Sainsbury's said switching to bags could save 1,400 tonnes of packaging a year and is now considering using it more widely across its milk range.

Senior dairy buyer Emma Metcalf-King said colleagues had been given free jugs before the launch to help them better explain the system to customers.

"This, coupled with the fact that our customers want to do the right thing for the environment, has driven sales way ahead of our expectations," she said.

Meanwhile, Waitrose decided two months ago to stop selling milk in pouches because "poor demand led to high levels of milk being wasted".

"It was a very hard decision to take but we believe it's totally unacceptable for food to be wasted in this way, so instead we will continue our work to minimise packaging in other ways," Waitrose said in a statement.

The retailer highlighted the increased recycled content in its standard plastic milk bottles – meaning that hundreds of tonnes of plastic are reused every year – as an example of its work to reduce the environmental impact of its packaging.

Waitrose launched the milk jug across all its stores in the summer of 2007.