Asda has moved to allay British egg producers' concerns about illegal egg imports by pledging to work with its suppliers to ensure none of its products will contain egg from battery cages as of next year.

An EU-wide ban on battery cages comes into force in January 2012, but not all EU countries will be ready to comply, raising fears that UK producers could be undercut by cheaper battery imports from abroad.

Asda said it was talking to its supply base about how to implement an appropriate auditing and traceability regime to ensure all liquid egg in its products came from enriched cages. All shell eggs sold by Asda are British, making it relatively easy to verify which rearing systems they came from. But products using liquid egg can be trickier to trace, given EU cross-border trade.

Sainsbury's said all its suppliers would be legally required to use legal liquid egg as of 2012.