The Scottish government has warned retailers they face legislation on plastic bag waste if voluntary action proves unsuccessful.

Rural affairs and environment secretary Richard Lochhead told the Scottish Parliament he was eager to find out what impact a UK-wide voluntary agreement on carrier bags was having.

The first substantial results of the initiative - set up nearly a year ago to reduce the impact of carrier bags on the environment by 25% - are due next month.

"If the results are poor we will take further action," said Lochhead.

The government would consult shortly on potential legislative measures in support of a 'zero waste' strategy, he added.

"We may legislate and may follow the approach taken by California and require retailers to take back and recycle plastic grocery bags."

Lochhead said he hoped a meeting with the chief executives of all major supermarket chains to discuss waste would take place within the next two months.