Dutch and Belgian investigators launched joint raids on Thursday over Europe's insecticide-tainted egg scare as Britain said it had imported far more contaminated eggs than originally revealed.

The spiralling scandal also spread to an eighth country, Luxembourg, which announced that it too had found eggs containing the insecticide fipronil, which can be harmful to human health.

Millions of eggs have been destroyed or taken off the shelves across Europe with growing questions about the extent to which consumers have been kept in the dark over the scale of the problem.

Fipronil is commonly used to get rid of fleas, lice and ticks from animals but is banned by the EU from use in the food industry. It can harm people's kidneys, liver and thyroid glands.

In the Netherlands and Belgium, the countries at the epicentre of the scare, authorities said they carried out coordinated searches at several premises linked to a fraud probe about how fipronil got into the food chain.

"There are several raids being held in The Netherlands, in conjunction with the Belgians," Dutch public prosecution service spokeswoman Marieke van der Molen told AFP, but declined to give further details.

A spokeswoman for the prosecutor in Belgium's northern port city of Antwerp said in a statement: "In connection with the fipronil case, several raids are currently being carried out."

The joint action came despite Belgium one day earlier accusing the Netherlands of knowing about the problem of fipronil in eggs since November 2016, but failing to inform them until July.

The Belgian searches took place at eight sites in the Flanders region of Belgium, near the border with the Netherlands, Het Laatste Nieuws newspaper reported.

- Britain boost egg numbers -

Meanwhile British authorities said that around 700,000 eggs from Dutch farms implicated in the scandal had been distributed in Britain, just days after saying the number was only 21,000.

As a result, four major British supermarket chains have withdrawn some products containing eggs, including sandwiches and salads, the Food Standards Agency said.

"It is likely that the number of eggs that have come to the UK is closer to 700,000 than the 21,000 we previously believed had been imported," the agency said, adding that this represents just 0.007 percent of the eggs consumed in Britain every year and playing down the risk to public health.

Luxembourg said that eggs sold in branches of the discount supermarket Aldi had been withdrawn, with one batch containing so much fipronil it was unsafe to be eaten by young children. Aldi earlier this month pulled all Dutch eggs from its stores in Germany.

Tests also found fipronil in eggs sold in Luxembourg supermarket chain Cactus, which had originally come from the Netherlands, while two Luxembourg suppliers of prepared meals, Caterman and Carnesa, said they had received cartons of liquid eggs from a contaminated source in Belgium.

Some of those eggs had been used in minced beef and luncheon meat but the items had been removed, they said.

The eggs at the centre of the scandal have mainly come from the Netherlands, followed by Belgium and Germany. Dozens of farms have been shut.

Sweden, Switzerland, Britain, France and Luxembourg have also now announced that they have found contaminated eggs.

The problem is believed to stem from a substance used by Dutch company Chickfriend which farmers in the Netherlands and Belgium say they hired to treat their chickens.

A lawyer for a Belgian company, Poultry-Vision, says the firm sold it to Chickfriend but has not said where it got the substance.

The French government says a Belgian company -- which it did not identify -- mixed fipronil with another, lawful, substance.

Source: AFP