Almost one in five lettuces has traces of pesticides above acceptable levels, tests made in the past year reveal.
A small number were also found with chemicals not approved for use on the vegetable in Britain. Green campaigners used the results to renew calls for tougher measures to protect consumers' health.
The Pesticide Safety Directorate tested 153 samples of winter lettuce between November 2001 and January. Twenty-seven samples were found with enough pesticides to put them over the maximum residue level – a guideline rather than a safety limit. Pesticides without a licence for use on lettuces were found on nine samples.
Sandra Bell, of Friends of the Earth, said the results were "disturbing". She added: "The voluntary approach to reducing pesticide use is failing."