Britain's leading supermarkets are giving out 418 million fewer plastic bags a month than they were three years ago, but still just failed to meet a target to cut the number by half.

Last December, the seven leading high street supermarkets signed up to a voluntary deal with to reduce the number of carrier bags handed out by 50 per cent compared to 2006 figures.

The government said the supermarkets had reduced the number of bags from 870 million to 452 million, a cut of 48 per cent.

"This is a great achievement by the seven supermarkets and their customers and it shows that by working together, we really can change our bag habits," said Environment Secretary Hilary Benn.

"The target of a 50 per cent reduction was only narrowly missed and retailers have really put a lot into this in the last six months."

Environmentalists say plastic bags can take up to 1,000 years to disintegrate and pose threats to marine life, birds and other animals, while most end up as landfill waste.

Last year Prime Minister Gordon Brown had warned retailers to take action on the issue or the government might force them to charge shoppers for their bags.

A survey in April showed that each shopper went through 13,000 bags in a lifetime.

The British Retail Consortium said the reduction had been achieved through schemes which worked for their customers.

"These figures send a clear message: the voluntary approach is very successful and can lead to better informed customers and lasting change," said Stephen Robertson, the BRC director general.

"Changing customer habits on this scale, this quickly, isn't easy. But it's a huge testament to customers, who've switched to bags for life and cut bag usage."