Cancer-causing chemicals have been found in nearly one in four samples of soy sauce and other Chinese flavourings tested by food watchdogs, it was announced yesterday.

In some, the levels massively exceeded international safety limits while others contained traces of a banned toxic substance.

Yesterday officials issued a \'hazard alert\' and demanded that supermarket shelves be cleared of the products and that consumers and caterers throw out the offending brands.

The list also includes varieties of oyster sauce, mushroom sauce and a chicken marinade. All are likely to be used in Chinese or Thai restaurants.

Virtually all the brands involved were imported from Thailand, China, Taiwan and Hong Kong, and sold through specialist Chinese supermarkets. None of those sold by major retailers contained the chemicals.

The Food Standards Agency, which carried out the tests, believes the most likely buyers will be Chinese and Thai restaurants and families from Eastern and South East Asian backgrounds.

It stressed that occasional users were unlikely to be harmed but there was a concern for people consuming high levels of the products.

The samples involved in the survey of 100 products were collected more than five months ago.

Explaining the delay in publishing the findings, the FSA said it had to run a detailed analysis, contact importers and trace the history of consignments. The chemical 3-MCPD is considered so dangerous that the EU will not allow any more than the tiniest amount in food - just 0.02 mg per kg.

Yet one of the products, sold under the brand name Golden Mountain, contained close to 5,000 times that figure. Just two teaspoons would be equivalent to 20 times the acceptable daily intake recommended for a woman.

The survey also revealed traces of an even more harmful chemical, 1,3-DCP, which is banned from all food because it is toxic to genes, as well as carcinogenic.

Some 24 of the 100 samples were positive for 3-MCPD and two thirds of these had traces of 1,3-DCP. The two are thought to create a higher risk of liver cancer.

FSA deputy chairman Suzi Leather said: \'Soy sauce can be produced without these chemicals and we expect swift action from the industry to ensure that the planned EU legal limits are met.\' The shops the FSA tested were concentrated in Leeds, Manchester, London and Cambridge. However, the brands are likely to be available nationwide.

The products carried the brand names Golden Mountain, King Imperial, Pearl River Bridge, Jammy Chai, Golden Mark, Kimlan, Lee Kum Kee, Tung Chun, Sinsin and Golden Swan.

Some of the makers and importers have claimed that they were the victims of counterfeiters.