UK health officials are calling for tighter controls against cancer-causing chemicals that have been found in peanut butter. The call comes after scientific studies showed that some peanut butter on sale in the UK contained excessive levels of aflatoxins, a naturally occurring contaminant. In an exclusive study commissioned by the BBC, one product from the UK supermarket chain Tesco had more than twice the maximum level of aflatoxins permitted under EU safety rules. According to trading standards officers, the current controls are not enough to prevent contaminated nuts from entering the country and urgent action is needed. The problem occurs when peanuts are contaminated by a fungus that produces toxins linked to liver cancer. The problem is the fungus occurs randomly: one jar of peanut butter may contain high levels of aflatoxins, while another from the same batch may not. Public health analyst Peter Brown said it had been "a particularly busy season" for peanut imports found to be affected. According to port health officers in Felixstowe, last year, they have condemned 30 out of 250 peanut consignments. Another 40 were deemed unsafe for human consumption without further processing. In a report disclosed exclusively to the BBC, Suffolk Trading Standards found that one fourth of the peanut butter samples tested contained excessive levels of aflatoxins. The BBC then conducted another study, sending 17 different types of peanut butter to the public analyst. 14 contained aflatoxins, although most were within the legal limit of two micrograms per kilogram. When tested, some jars of Tesco's 25 per cent less fat smooth peanut contained 4.2 micrograms per kilogram of aflatoxins. According to the supermarket chain, the problem is a challenge for the whole industry. It expressed concern that in spite of its extensive controls affected nuts appeared to have got into its product. Professor David Phillips from the Institute of Cancer Research said the level of chemicals being talked about posed only "the tiniest risk" to health. However he added: "The public has the right to know that limits have not been exceeded. And any product that has exceeded the limit should probably be taken off the market."