Sales of Sainbury’s milk bags, which use 75% less packaging than standard plastic bottles, have hit around 110,000 per week.

The bags now account for one in every ten two-pint semi-skimmed sold, twice as many as the supermarket originally predicted.

The bags have been introduced as part of Sainsbury’s drive to reduce packaging by a third by 2015. Switching to bags could save up to 1,400,000 kg of packaging every year.

Milk bags already account for more than half of milk sales in Canada, South Africa, China and Poland.

Sainsbury’s senior dairy buyer Emma Metcalf-King said: “Sales have far exceeded our expectations.”

The bags are made from very strong polyethylene and have undergone extensive testing to ensure their durability. Compared to an equivalent two pint plastic bottle, milk in a bag costs six pence less because it uses 75% less packaging and is cheaper to produce.