Sainsbury’s, Asda, Morrisons and Waitrose are withdrawing millions of products from shelves after it emerged 700,000 contaminated eggs have been distributed in the UK.

The Food Standards Agency (FSA) previously said that 21,000 eggs contaminated with the insecticide fipronil had been shipped to Britain from the Netherlands.

However the estimate has since been revised substantially amid warnings that some eggs may have been consumed already.

Food production ban

Fipronil is banned across the EU from use in the production of foodstuffs.

In large quantities it can damage kidneys, the liver and thyroid glands.

However, the chemical is considered to be only “moderately hazardous” by the World Health Organisation.

The fears over potential contamination have sparked the four supermarket giants into action, withdrawing from shelves salads, sandwiches and fillers that are thought to contain the infected eggs.

Fresh eggs are largely unaffected, with the contaminated eggs present in processed foods.

‘Unlikely risk to public health’

But the FSA said the eggs were imported to the UK between March and June, meaning the infected products would have already been eaten, and there was “unlikely” to be a risk to public health.

A spokesman added: “The decision to withdraw these products is not due to food safety concerns, but is based on the fact that fipronil is not authorised for use in food producing animals.

“The FSA and Food Standards Scotland are committed to ensuring that food is safe and that UK consumers have food they can trust.”

Dutch investigators have detained two men suspected of being involved in the illegal use of pesticide at the poultry farms.

It has sparked a food safety scare in a number of European countries, including Germany, where Aldi and Lidl have been forced to remove millions of eggs from sale.