London: Millions of families will miss out on a longstanding Christmas tradition this year as supermarkets refuse to stock Brazil nuts.

The nuts, popular with afternoon tea around the Christmas tree, have been judged a potential safety risk by the European Commission.

Traces of a toxin that can cause liver cancer have been found in their shells. So the EC has decreed every batch imported from Brazil must be tested for the substance aflatoxin.

Supermarkets claim the cost of destroying any shipments would be too high and are not willing to import them.

Brazil nut kernels, used in nut mixtures and chocolate Brazil nuts, can still be imported from Bolivia and Peru.

But the Combined Edible Nut Trade Association said that Brazil is the only country to export the nuts in the shell.

‘Commercially it is now too risky to import them. The EU have put overly stringent limits on this without really good evidence,’ said the association’s chairman Peter Morgan.

The European limit on aflatoxin levels in Brazil nuts is four parts per billion but Mr Morgan said the U.S. limit is 15 parts per billion.

EC officials say levels 100 times higher than the limit have been found. They fear the substance, caused by contaminating fungi, could pass from the shell to the nut, and then be consumed.

A spokesman said: ‘We would like to lift the restrictions but we are not yet satisfied the Brazilian authorities have taken the correct measures to show they are safe.’

Brazilian embassy commercial spokesman Eduardo Barbosa said: ‘They are harvested by forest people in the Amazon, for whom this ban will have a big impact.’

Sainsbury’s said: ‘This is an industry-wide issue and we are not stocking Brazil nuts in the shell but we are still selling Brazil nut kernels.’