The salmonella food poisoning bug found in Cadbury chocolate may have contaminated up to 30 different brands, food safety officials have warned.

Safety tests are now being carried out on a wide range of bars after it emerged that the contamination, which was caused by a leaking pipe discovered earlier this year at a Cadbury plant, may have been far greater than first realised. More than one million Cadbury chocolate bars were withdrawn from sale 10 days ago after the firm admitted that chocolate "crumb" was contaminated with traces of salmonella montevideo, a rare strain of the bug, six months ago.

Health officials in Birmingham are now testing another 30 brands and the Food Standards Agency has warned that other types of Cadbury chocolate could be withdrawn.