The FSA said the illegal dye, which triggered a giant recall in February, is now known to sometimes be created as a by-product during the manufacturing of permitted dye Sunset Yellow.
It has not ruled out the chances of Sudan 1 appearing again as a by-product in other dyes permitted for use under EU legislation.
Sunset Yellow is used in confectionery, such as Smarties, soft drinks, chocolate products, sauces, seasonings and pickles. A spokeswoman for Nestlé Rowntree, the maker of Smarties, confirmed it used Sunset Yellow but refused to comment. “This is an industry-wide matter,” she added.
Currently, under EU laws, it is acceptable to have up to 5% of a subsidiary or secondary colouring present in permitted dyes. However, many food grade chemical dyes, such as Sunset Yellow, can contain up to 30% impurities, said Howard Davies, laboratory manager for Campden & Chorleywood Food Research Association.